Methodological challenges in causal research on racial and ethnic patterns of cognitive trajectories: measurement, selection, and bias

Adult Child Financial Disadvantage and the Cognitive Trajectories Among Older Parents in the United States

OBJECTIVES

Adult child socioeconomic status (SES) has been identified as a predictor of older parents' cognitive aging. However, studies have primarily relied on educational attainment as the sole measure of adult child SES. We evaluated the relationship between adult children's financial disadvantage and cognitive outcomes of older parents in the United States.

METHODS

We used data from U.S. Health and Retirement Study (2000-2014, n = 15,053 respondents ≥51 years with at least 1 adult child). Adult child financial disadvantage was measured with 3 indicators of extremely low income, unemployment, and lack of homeownership. We used linear mixed models to estimate the association between adult child financial disadvantage and the rate of decline in verbal memory scores, controlling for respondents' sociodemographic characteristics.

RESULTS

Having at least 1 adult child (vs no adult children) with extremely low income was found to be associated with lower verbal memory (b = -0.041, 95% confidence interval [CI]: -0.043, -0.039) at baseline. There was a small but significant association with the rate of decline in verbal memory z-scores (b = 0.004, 95% CI: 0.000, 0.008) and some evidence of heterogeneity by parent gender, marital status, and SES.

DISCUSSION

Offspring financial disadvantage may be influential for older parents' initial level of memory function, although evidence of associations with memory decline was weak. Public policy interventions aimed at improving the economic conditions of adult children may indirectly benefit the cognitive performance of disadvantaged parents in their later life.

Confounder Selection and Sensitivity Analyses to Unmeasured Confounding from Epidemiological and Statistical Perspectives

In observational studies, identifying and adjusting for a sufficient set of confounders is crucial for accurately estimating the causal effect of the exposure on the outcome. Even in studies with large sample sizes, which typically benefit from small variances in estimates, there is a risk of producing estimates that are precisely inaccurate if the study suffers from systematic errors or biases, including confounding bias. To date, several approaches have been developed for selecting confounders. In this article, we first summarize the epidemiological and statistical approaches to identify a sufficient set of confounders. Particularly, we introduce the modified disjunctive cause criterion as one of the most useful approaches, which involves controlling for any pre-exposure covariate that affects the exposure, outcome, or both. It then excludes instrumental variables but includes proxies for the shared common cause of exposure and outcome. Statistical confounder selection is also useful when dealing with a large number of covariates, even in studies with small sample sizes. After introducing several approaches, we discuss some pitfalls and considerations in confounder selection, such as the adjustment for instrumental variables, intermediate variables, and baseline outcome variables. Lastly, as it is often difficult to comprehensively measure key confounders, we introduce two statistics, E-value and Robustness value, for assessing sensitivity to unmeasured confounders. Illustrated examples are provided using the National Health and Nutritional Examination Survey Epidemiologic Follow-up Study. Integrating these principles and approaches will enhance our understanding of confounder selection and facilitate better reporting and interpretation of future epidemiological studies.

A Subtype Perspective on Cognitive Trajectories in Healthy Aging

Cognitive aging is a complex and dynamic process characterized by changes due to genetics and environmental factors, including lifestyle choices and environmental exposure, which contribute to the heterogeneity observed in cognitive outcomes. This heterogeneity is particularly pronounced among older adults, with some individuals maintaining stable cognitive function while others experience complex, non-linear changes, making it difficult to identify meaningful decline accurately. Current research methods range from population-level modeling to individual-specific assessments. In this work, we review these methodologies and propose that population subtyping should be considered as a viable alternative. This approach relies on early individual-specific detection methods that can lead to an improved understanding of changes in individual cognitive trajectories. The improved understanding of cognitive trajectories through population subtyping can lead to the identification of meaningful changes and the determination of timely, effective interventions. This approach can aid in informing policy decisions and in developing targeted interventions that promote cognitive health, ultimately contributing to a more personalized understanding of the aging process within society and reducing the burden on healthcare systems.

Associations between Rest-Activity Rhythms and Liver Function Tests: The US National Health and Nutrition Examination Survey, 2011-2014

Liver functions are regulated by the circadian rhythm; however, whether a weakened circadian rhythm is associated with impaired liver function is unclear. This study aims to investigate the association of characteristics of rest-activity rhythms with abnormal levels of biomarkers of liver function. Data were obtained from the National Health and Nutrition Examination Survey 2011-2014. Seven rest-activity rhythm parameters were derived from 24 h actigraphy data using the extended cosine model and non-parametric methods. Multiple logistic regression and multiple linear regression models were used to assess the associations between rest-activity rhythm parameters and alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), gamma-glutamyl transaminase (GGT), albumin and bilirubin. Weakened overall rhythmicity characterized by a lower F statistic was associated with higher odds of abnormally elevated ALP (ORQ1vs.Q5: 2.16; 95% CI 1.19, 3.90) and GGT (ORQ1vs.Q5: 2.04; 95% CI 1.30, 3.20) and abnormally lowered albumin (ORQ1vs.Q5: 5.15; 95% CI 2.14, 12.38). Similar results were found for a lower amplitude, amplitude:mesor ratio, interdaily stability and intradaily variability. Results were robust to the adjustment of confounders and cannot be fully explained by individual rest-activity behaviors, including sleep and physical activity. Weakened rest-activity rhythms were associated with worse liver function as measured by multiple biomarkers, supporting a potential role of circadian rhythms in liver health.

Semantic item-level metrics relate to future memory decline beyond existing cognitive tests in older adults without dementia

In normal aging, the cognitive domain of semantic memory remains preserved, while the domain of episodic memory declines to some extent. In Alzheimer's disease dementia, both semantic and episodic memory become impaired early in the disease process. Given the need to develop sensitive and accessible cognitive markers for early detection of dementia, we investigated among older adults without dementia whether item-level metrics of semantic fluency related to episodic memory decline above and beyond existing neuropsychological measures and total fluency score. Participants were drawn from the community-based Washington Heights-Inwood Columbia Aging Project cohort (N = 583 English speakers, Mage = 76.3 ± 6.8) followed up to five visits across up to 11 years. We examined the association of semantic fluency metrics with subsequent declines in memory performance using latent growth curve models covaried for age and recruitment wave. Results showed that item-level metrics (e.g., lexical frequency, age of acquisition, and semantic neighborhood density) were associated with a decline in episodic memory-even when covarying for other cognitive tests-while the standard total score was not. Moderation analyses showed that the relationship of semantic fluency metrics with memory decline did not differ across race, sex/gender, or education. In conclusion, item-level data hold a wealth of information with potential to reveal subtle semantic memory impairment, which tracks with episodic memory impairment, among older adults without dementia beyond existing neuropsychological measures. Implementation of psycholinguistic metrics may point to cognitive tools that have better prognostic value or are more sensitive to cognitive change in the context of clinical trials or observational studies. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Racialized experience, biomarkers of lead exposure, and later-life cognition: a mediation analysis

We evaluated the role of the neurotoxicant lead (Pb) in mediating racial disparities in later-life cognition in 1,085 non-Hispanic Black and 2,839 non-Hispanic white participants in NHANES (1999-2002, 2011-2014) 60+ years of age. We operationalized Black race as a marker for the experience of racialization and exposure to systemic racism. We estimated patella bone Pb via predictive models using blood Pb and demographics. Concurrent cognition (processing speed, sustained attention, working memory) was measured by the Digit Symbol Substitution Test (DSST) and a global measure combining four cognitive tests. To obtain the portion mediated, we used regression coefficients (race on Pb * Pb on cognitive score)/(race on cognitive score), adjusting for age, NHANES cycle, and sample weights. Other confounder adjustment (education, poverty income ratio, smoking) was limited to the mediator-outcome (i.e., Pb-cognition) pathway because these factors do not lie upstream of race and so cannot confound associations with race. Pb was estimated to mediate 0.6% of the association between race and global cognition, and 4% of the DSST. Our results suggest that later-life cognitive health disparities may be impacted by avoidable lead exposure driven by environmental injustice, noting that a large proportion of the pathway of systemic racism harming cognition remains.

Instrumental activities of daily living trajectories and risk of mild cognitive impairment among Chinese older adults: results of the Chinese longitudinal healthy longevity survey, 2002-2018

Background

The association between the instrumental activities of daily living (IADL) score and the risk of initial cognitive function impairment is inconclusive. We aimed to identify distinctive IADL trajectories and examine their relationship with the onset of mild cognitive impairment (MCI) among Chinese older people.

Methods

The study used six-wave longitudinal data from the Chinese Longitudinal Healthy Longevity Survey conducted between 2002 and 2018. It included a total of 11,044 Chinese people aged 65 years or older. A group-based trajectory model was used to identify distinctive trajectories of the IADL score, and the Cox proportional hazards model was used to explore the hazard ratio of various trajectories at the onset of MCI. Interaction analysis was used to analyze individual modification between the IADL trajectories and the onset of MCI. Finally, we adopted four types of sensitivity analysis to verify the robustness of the results.

Results

During a median follow-up of 16 years, the incidence of MCI was 6.29 cases per 1,000 person-years (95% confidence interval [CI] 5.92-6.68). Three distinct IADL trajectory groups were identified: a low-risk IADL group (41.4%), an IADL group with increasing risk (28.5%), and a high-risk IADL group (30.4%). Using the Cox proportional hazards model after adjusting for covariates, we found that compared with the low risk IADL group, the hazard ratio of the IADL group with increasing risk was 4.49 (95% CI = 3.82-5.28), whereas that of the high-risk IADL group was 2.52 (95% CI 2.08-3.05). Treating the IADL group with increasing risk as the reference, the hazard ratio for the high-risk IADL group was 0.56 (95% CI 0.48-0.66). Interaction analyses showed that age and residence were significant moderators (P for interaction <0.05).

Conclusion

A group-based trajectory model was developed to classify older people into three distinct trajectory groups of the IADL score. The IADL group with increasing risk had a greater risk of MCI than the high-risk IADL group. In the IADL group with increasing risk, city residents of ≥80 years were the most likely to develop MCI.

Brain Aging Among Racially and Ethnically Diverse Middle-Aged and Older Adults

Importance

Neuroimaging studies have documented racial and ethnic disparities in brain health in old age. It remains unclear whether these disparities are apparent in midlife.

Objective

To assess racial and ethnic disparities in magnetic resonance imaging (MRI) markers of cerebrovascular disease and neurodegeneration in midlife and late life.

Design, Setting, and Participants

Data from 2 community-based cohort studies, Washington Heights-Inwood Columbia Aging Project (WHICAP) and the Offspring Study of Racial and Ethnic Disparities in Alzheimer Disease (Offspring), were used. Enrollment took place from March 2011 and June 2017, in WHICAP and Offspring, respectively, to January 2021. Of the 822 Offspring and 1254 WHICAP participants approached for MRI scanning, 285 and 176 refused participation in MRI scanning, 36 and 76 were excluded for contraindications/ineligibility, and 4 and 32 were excluded for missing key variables, respectively.

Main Outcomes and Measures

Cortical thickness in Alzheimer disease-related regions, white matter hyperintensity (WMH) volume.

Results

The final sample included 1467 participants. Offspring participants (497 [33.9%]) had a mean (SD) age of 55 (10.7) years, had a mean (SD) of 13 (3.5) years of education, and included 117 Black individuals (23.5%), 348 Latinx individuals (70%), 32 White individuals (6.4%), and 324 women (65.2%). WHICAP participants (970 [66.1%]) had a mean (SD) age of 75 (6.5) years, had a mean (SD) of 12 (4.7) years of education, and included 338 Black individuals (34.8%), 389 Latinx individuals (40.1%), 243 White individuals (25.1%), and 589 women (65.2%). Racial and ethnic disparities in cerebrovascular disease were observed in both midlife (Black-White: B = 0.357; 95% CI, 0.708-0.007; P = .046) and late life (Black-Latinx: B = 0.149, 95% CI, 0.068-0.231; P < .001; Black-White: B = 0.166; 95% CI, 0.254-0.077; P < .001), while disparities in cortical thickness were evident in late life only (Black-Latinx: B = -0.037; 95% CI, -0.055 to -0.019; P < .001; Black-White: B = -0.064; 95% CI -0.044 to -0.084; P < .001). Overall, Black-White disparities were larger than Latinx-White disparities for cortical thickness and WMH volume. Brain aging, or the association of age with MRI measures, was greater in late life compared with midlife for Latinx (cortical thickness: B = 0.006; 95% CI, 0.004-0.008; P < .001; WMH volume: B = -0.010; 95% CI, -0.018 to -0.001; P = .03) and White (cortical thickness: B = 0.005; 95% CI, 0.002-0.008; P = .001; WMH volume: B = -0.021; 95% CI -0.043 to 0.002; P = .07) participants but not Black participants (cortical thickness: B = 0.001; 95% CI, -0.002 to 0.004; P =.64; WMH volume: B = 0.003; 95% CI, -0.010 to 0.017; P = .61), who evidenced a similarly strong association between age and MRI measures in midlife and late life.

Conclusions and Relevance

In this study, racial and ethnic disparities in small vessel cerebrovascular disease were apparent in midlife. In Latinx and White adults, brain aging was more pronounced in late life than midlife, whereas Black adults showed accelerated pattern of brain aging beginning in midlife.

Survival Benefit of First Single-Organ Deceased Donor Kidney Transplantation Compared With Long-term Dialysis Across Ages in Transplant-Eligible Patients With Kidney Failure

IMPORTANCE

Kidney transplant is considered beneficial in terms of survival compared with continued dialysis for patients with kidney failure. However, randomized clinical trials are infeasible, and available evidence from cohort studies is at high risk of bias.

OBJECTIVE

To compare restricted mean survival times (RMSTs) between patients who underwent transplant and patients continuing dialysis across transplant candidate ages and depending on waiting time, applying target trial emulation methods.

DESIGN, SETTING, AND PARTICIPANTS

In this retrospective cohort study, patients aged 18 years or older appearing on the wait list for their first single-organ deceased donor kidney transplant between January 1, 2000, and December 31, 2018, in Austria were evaluated. Available data were obtained from the Austrian Dialysis and Transplant Registry and Eurotransplant and included repeated updates on wait-listing status and relevant covariates. Data were analyzed between August 1, 2019, and December 23, 2021.

EXPOSURES

A target trial was emulated in which patients were randomized to either receive the transplant immediately (treatment group) or to continue dialysis and never receive a transplant (control group) at each time an organ became available.

MAIN OUTCOMES AND MEASURES

The primary outcome was time from transplant allocation to death. Effect sizes in terms of RMSTs were obtained using a sequential Cox approach.

RESULTS

Among the 4445 included patients (2974 men [66.9%]; mean [SD] age, 52.2 [13.2] years), transplant was associated with increased survival time across all considered ages compared with continuing dialysis and remaining on the wait list within a 10-year follow-up. The estimated RMST differences were 0.57 years (95% CI, -0.14 to 1.84 years) at age 20 years, 3.01 years (95% CI, 2.50 to 3.54 years) at age 60 years, and 2.48 years (95% CI, 1.88 to 3.04 years) at age 70 years. The survival benefit for patients who underwent transplant across ages was independent of waiting time.

CONCLUSIONS AND RELEVANCE

The findings of this study suggest that kidney transplant prolongs the survival time of persons with kidney failure across all candidate ages and waiting times.

Association between blood lead levels and hyperlipidemiais: Results from the NHANES (1999-2018)

Background

Research on the association between blood lead (Pb) and lipid biomarkers have yielded inconsistent results, and epidemiological studies on blood Pb levels and hyperlipidemia are scarce. The present study aimed to examine the association between blood Pb levels and hyperlipidemia in adults from the National Health and Nutrition Examination Survey (NHANES).

Methods

A total of 43,196 participants in the NHANES from 1999 to 2018 were included in the final analysis. Hyperlipidemia was determined based on the National Cholesterol Education Program guidelines. Blood Pb levels were assessed using inductively-coupled plasma mass spectrometry. Weighted multivariable logistic regression analysis and subgroup analysis were conducted to determine the correlation between blood Pb levels and hyperlipidemia.

Results

In the multivariable logistic regression model, high blood Pb levels were significantly associated with hyperlipidemia after adjusting for confounders (OR 1.41; 95%CI: 1.18-1.67). Furthermore, elevated blood Pb levels were associated with an increased risk of hyperlipidemia across the four quartile (Q) groups (Q1: OR 1.00; Q2: OR 1.16 [95%CI: 1.04-1.29]; Q3: OR 1.39 [95%CI: 1.21-1.59]; and Q4: OR 1.33 [95%CI: 1.15-1.54]; P for trend <0.05). Significant moderating effects were found in the subgroup analysis stratified by age, education, hypertension, and diabetes (P < 0.05). In sensitivity analysis, the ORs for hyperlipidemia across the quartiles of blood Pb levels were 1.00, 1.17 (95%CI: 1.05-1.30), 1.42 (95%CI: 1.24-1.62), and 1.38 (95%CI: 1.19-1.60) for Q1, Q2, Q3, and Q4, respectively (P for trend <0.001) after removing adults with arteriosclerotic cardiovascular disease, and the ORs were 1.00, 1.13 (95%CI: 1.01-1.25), 1.38 (95%CI: 1.21-1.56), and 1.32 (95%CI: 1.16-1.52) for Q1, Q2, Q3, and Q4, respectively (P for trend <0.001) after including pregnant women.

Conclusion

The current study showed a positive association between blood lead levels and hyperlipidemia.

The effect of missing data and imputation on the detection of bias in cognitive testing using differential item functioning methods

Background

Item response theory (IRT) methods for addressing differential item functioning (DIF) can detect group differences in responses to individual items (e.g., bias). IRT and DIF-detection methods have been used increasingly often to identify bias in cognitive test performance by characteristics (DIF grouping variables) such as hearing impairment, race, and educational attainment. Previous analyses have not considered the effect of missing data on inferences, although levels of missing cognitive data can be substantial in epidemiologic studies.

Methods

We used data from Visit 6 (2016–2017) of the Atherosclerosis Risk in Communities Neurocognitive Study (N = 3,580) to explicate the effect of artificially imposed missing data patterns and imputation on DIF detection.

Results

When missing data was imposed among individuals in a specific DIF group but was unrelated to cognitive test performance, there was no systematic error. However, when missing data was related to cognitive test performance and DIF group membership, there was systematic error in DIF detection. Given this missing data pattern, the median DIF detection error associated with 10%, 30%, and 50% missingness was -0.03, -0.08, and -0.14 standard deviation (SD) units without imputation, but this decreased to -0.02, -0.04, and -0.08 SD units with multiple imputation.

Conclusions

Incorrect inferences in DIF testing have downstream consequences for the use of cognitive tests in research. It is therefore crucial to consider the effect and reasons behind missing data when evaluating bias in cognitive testing.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12874-022-01572-2.

The long arm of childhood socioeconomic deprivation on mid- to later-life cognitive trajectories: A cross-cohort analysis

Introduction

Earlier studies of the effects of childhood socioeconomic status (SES) on later-life cognitive function consistently report a social gradient in later-life cognitive function. Evidence for their effects on cognitive decline is, however, less clear.

Methods

The sample consists of 5324 participants in the Whitehall II study, 8572 in the Health and Retirement Study (HRS), and 1413 in the Kame Project, who completed self-report questionnaires on their early life experiences and underwent repeated cognitive assessments. We characterized cognitive trajectories using latent class mixed models, and explored associations between childhood SES and latent class membership using logistic regressions.

Results

We identified distinct trajectories classes for all cognitive measures examined. Childhood socioeconomic deprivation was associated with an increased likelihood of being in a lower trajectory class.

Discussion

Our findings support the notions that cognitive aging is a heterogeneous process and early life circumstances may have lasting effects on cognition across the life-course.

Quality and Location of the Surgical Episode Mediate a Large Proportion of Socioeconomic-Based Survival Disparities in Patients with Resected Stage I-III Colon Cancer

INTRODUCTION

Lower socioeconomic status (SES) is associated with shorter overall survival (OS) in patients with locoregional colon cancer. We aimed to estimate: (1) the proportion of SES-based OS disparities mediated by disparities in the quality and location of surgical treatment in patients with resected stage I-III colon cancer and (2) the relative importance of components of surgical quality.

PATIENTS AND METHODS

We examined patients ages 18-80 years with resected stage I-III colon adenocarcinoma using the 2010-2016 National Cancer Database. SES was defined at the zip code level. Inverse odds weighting mediation analysis was used to estimate the proportion mediated (PM) for nine treatment quality-related and facility-related factors and composite PMs in models including all nine mediators. Models compared high SES patients with each lower SES stratum.

RESULTS

Among 171,009 patients, 5-year OS increased from 70.4% in low SES patients to 78.1% in high SES. When high SES patients were compared with low, lower-middle, and upper-middle SES patients, PM ranges among lower SES strata were: minimally invasive surgery 16.0-16.6%, lymph nodes examined 7.7-9.6%, positive margins 3.8-6.5%, length of stay 16.7-28.1%, readmissions insignificant to 3.7%, treatment at > 1 CoC facility 2.7-3.1%, facility type insignificant to 7.3%, facility volume 2.9-8.2%, and adjusted facility 90-day mortality rates 33.2-42.8%. Composite PMs were 76.9% (95% CI 61.3%, 92.4%) for low SES, 68.7% (95% CI 56.4%, 81.1%) for lower-middle SES, and 60.9% (95% CI 43.1%, 78.6%) for upper-middle SES.

CONCLUSIONS

These data suggest that improving the quality of the surgical episode for disadvantaged patients undergoing resection for locoregional colon cancer could decrease SES-based survival disparities by over half.

Deaths with Dementia in Indigenous and Non-Indigenous Australians: A Nationwide Study

BACKGROUND

The prevalence of dementia is generally reported to be higher among Indigenous peoples.

OBJECTIVE

The rates and coding of dementia mortality were compared between Indigenous and non-Indigenous Australians.

METHODS

De-identified individual records on causes of death for all people aged 40 years or more who died in Australia between 2006 and 2014 (n = 1,233,084) were used. There were 185,237 records with International Classification of Diseases, Tenth Revision, codes for dementia (Alzheimer's Disease, vascular dementia, or unspecified dementia) as the underlying cause of death or mentioned elsewhere on the death certificate. Death rates were compared using Poisson regression. Logistic regression was used to assess whether dementia was more likely to be classified as 'unspecified' type in Indigenous Australians.

RESULTS

The rates of death with dementia were 57% higher in Indigenous Australians, compared to non-Indigenous, relative rate (RR) 1.57, 95% confidence interval (CI) (1.48, 1.66), p < 0.0001. This excess of deaths was highest at ages below 75 (RRs > 2, test for interaction p < 0.0001), and among men (test for interaction p < 0.0001). When the underreporting of Indigenous status on the death certificate was taken into account the relative rate increased to 2.17, 95% CI (2.07, 2.29). Indigenous Australians were also more likely to have their dementia coded as 'unspecified' on their death certificate (Odds Ratio 1.92, 95% CI (1.66, 2.21), p < 0.0001), compared to the non-Indigenous group.

CONCLUSION

This epidemiological analysis based on population level mortality data demonstrates the higher dementia-related mortality rate for Indigenous Australians especially at younger ages.

Characterisation of neurodevelopmental and psychological outcomes in CHD: a research agenda and recommendations from the cardiac neurodevelopmental outcome collaborative

The Neurodevelopmental and Psychological Outcomes Working Group of the Cardiac Neurodevelopmental Outcome Collaborative was formed in 2018 through support from an R13 grant from the National Heart, Lung, and Blood Institute with the goals of identifying knowledge gaps regarding the neurodevelopmental and psychological outcomes of individuals with CHD and investigations needed to advance science, policy, clinical care, and patient/family outcomes. Accurate characterisation of neurodevelopmental and psychological outcomes in children with CHD will drive improvements in patient and family outcomes through targeted intervention. Decades of research have produced a generalised perspective about neurodevelopmental and psychological outcomes in this heterogeneous population. Future investigations need to shift towards improving methods, measurement, and analyses of outcomes to better inform early identification, prevention, and intervention. Improved definition of underlying developmental, neuropsychological, and social-emotional constructs is needed, with an emphasis on symptom networks and dimensions. Identification of clinically meaningful outcomes that are most important to key stakeholders, including patients, families, schools and providers, is essential, specifically how and which neurodevelopmental differences across the developmental trajectory impact stakeholders. A better understanding of the discontinuity and patterns of neurodevelopment across the lifespan is critical as well, with some areas being more impactful at some ages than others. Finally, the field needs to account for the impact of race/ethnicity, socio-economic status, cultural and linguistic diversity on our measurement, interpretation of data, and approach to intervention and how to improve generalisability to the larger worldwide population of patients and families living with CHD.

Adult child socio-economic status disadvantage and cognitive decline among older parents in Mexico

There is growing interest in the contribution of offspring educational attainment to parents' health outcomes. However, less is known about the impacts of offspring socio-economic status (SES) on parents' cognitive decline or about the role of offspring SES disadvantage. We used data from the Mexican Health and Aging Study (n = 10,426) to evaluate the impact of adult child SES disadvantage on parents' verbal memory trajectories over fourteen years (2001-2015). We estimated linear mixed models and used measures of adult child SES (educational, financial, and employment) disadvantage. Our most robust finding was that having an adult child with less than secondary education was associated with faster decline in verbal memory z-scores for older women (β: -0.009 [95% CI: -0.01, -0.001]) and men (β: -0.01 [95% CI: -0.02, -0.01]). Although poor adult child financial well-being was associated with a faster decline in parents' verbal memory z-scores, this finding was less consistent across model specifications. Additional analyses also suggested some evidence of heterogeneity by parents' own educational attainment and gender. These findings highlight the potential importance of children's socio-economic status for the cognitive aging of their older parents.

Inconsistent social rhythms are associated with abdominal adiposity after involuntary job loss: An observational study

Objective

Unemployment is an established risk factor for obesity. However, few studies have examined obesity-related health behavior after involuntary job loss specifically. Job loss confers a disruption in daily time structure that could lead to negative metabolic and psychological outcomes through chronobiological mechanisms. This study examines whether individuals with unstable social rhythms after involuntary job loss present with higher abdominal adiposity than individuals with more consistent social rhythms and whether this relationship varies as a function of depressive symptoms.

Methods

Cross-sectional baseline data (n = 191) from the ongoing Assessing Daily Activity Patterns in occupational Transitions (ADAPT) study were analyzed using linear regression techniques. Participants completed the Social Rhythm Metric-17 (SRM) daily over 2 weeks. They also completed the Beck Depression Inventory II (BDI-II) and participated in standardized waist circumference measurements (cm).

Results

A significant interaction emerged between SRM and BDI-II demonstrating that less consistent social rhythms were associated with larger waist circumference at lower levels of depressive symptoms. Additional exploratory analyses demonstrated a positive association between the number of daily activities performed alone and waist circumference when controlling for symptoms of depression.

Conclusion

These findings are the first to demonstrate a relationship between social rhythm stability and abdominal adiposity in adults who have recently, involuntarily lost their jobs. Results highlight the moderating role of depressive symptoms on daily routine in studies of metabolic health. Future prospective analysis is necessary to examine causal pathways.

Targeted metabolomics analysis of postoperative delirium

Postoperative delirium is the most common complication among older adults undergoing major surgery. The pathophysiology of delirium is poorly understood, and no blood-based, predictive markers are available. We characterized the plasma metabolome of 52 delirium cases and 52 matched controls from the Successful Aging after Elective Surgery (SAGES) cohort (N = 560) of patients ≥ 70 years old without dementia undergoing scheduled major non-cardiac surgery. We applied targeted mass spectrometry with internal standards and pooled controls using a nested matched case-control study preoperatively (PREOP) and on postoperative day 2 (POD2) to identify potential delirium risk and disease markers. Univariate analyses identified 37 PREOP and 53 POD2 metabolites associated with delirium and multivariate analyses achieved significant separation between the two groups with an 11-metabolite prediction model at PREOP (AUC = 83.80%). Systems biology analysis using the metabolites with differential concentrations rendered "valine, leucine, and isoleucine biosynthesis" at PREOP and "citrate cycle" at POD2 as the most significantly enriched pathways (false discovery rate < 0.05). Perturbations in energy metabolism and amino acid synthesis pathways may be associated with postoperative delirium and suggest potential mechanisms for delirium pathogenesis. Our results could lead to the development of a metabolomic delirium predictor.

The association of healthy behaviors with cognitive health expectancy in Chinese older adults: a population-based cohort study

OBJECTIVE

To examine how lifestyles and leisure activities are associated with cognitive health expectancy among older adults.

RESULTS

For young-old (aged 65), an absolute increase in life years without cognitive impairment was found among those with a healthy diet, engaging in mental activities and in social activities. For old-old (aged 85), an absolute increase was found for men engaging in physical activities besides those. Compared with counterparts in a high risk group, the young-old in a medium-low risk group had a smaller proportion of years without cognitive impairment. Old-old in a low risk group had a greater proportion.

CONCLUSION

Extra years of life gained by a healthy dietary pattern, mental activities, and social activities are free of cognitive impairment for both sexes across ages. The beneficial impact of individual and combined modifiable factors on cognitive health is most prominent in old-old.

METHODS

Data come from The Chinese Longitudinal Healthy Longevity Survey, a population-based cohort study of 27,193 participants aged 65+ conducted between 2002 and 2014. Smoking status, alcohol consumption, dietary pattern, marital status, physical, mental, social, and productive activities were assessed at baseline. Cognitive status was measured using the Chinese version of the MMSE.

Comparison of Mortality and Major Cardiovascular Events Among Adults With Type 2 Diabetes Using Human vs Analogue Insulins

Importance

The comparative cardiovascular safety of analogue and human insulins in adults with type 2 diabetes who initiate insulin therapy in usual care settings has not been carefully evaluated using machine learning and other rigorous analytic methods.

Objective

To examine the association of analogue vs human insulin use with mortality and major cardiovascular events.

Design, Setting, and Participants

This retrospective cohort study included 127 600 adults aged 21 to 89 years with type 2 diabetes at 4 health care delivery systems who initiated insulin therapy from January 1, 2000, through December 31, 2013. Machine learning and rigorous inference methods with time-varying exposures were used to evaluate associations of continuous exposure to analogue vs human insulins with mortality and major cardiovascular events. Data were analyzed from September 1, 2017, through June 30, 2018.

Exposures

On the index date (first insulin dispensing), participants were classified as using analogue insulin with or without human insulin or human insulin only.

Main Outcomes and Measures

Overall mortality, mortality due to cardiovascular disease (CVD), myocardial infarction (MI), stroke or cerebrovascular accident (CVA), and hospitalization for congestive heart failure (CHF) were evaluated. Marginal structural modeling (MSM) with inverse probability weighting was used to compare event-free survival in separate per-protocol analyses. Adjusted and unadjusted hazard ratios and cumulative risk differences were based on logistic MSM parameterizations for counterfactual hazards. Propensity scores were estimated using a data-adaptive approach (machine learning) based on 3 nested covariate adjustment sets. Sensitivity analyses were conducted to address potential residual confounding from unmeasured differences in risk factors across delivery systems.

Results

The 127 600 participants (mean [SD] age, 59.4 [12.6] years; 68 588 men [53.8%]; mean [SD] body mass index, 32.3 [7.1]) had a median follow-up of 4 quarters (interquartile range, 3-9 quarters) and experienced 5464 deaths overall (4.3%), 1729 MIs (1.4%), 1301 CVAs (1.0%), and 3082 CHF hospitalizations (2.4%). There were no differences in adjusted hazard ratios for continuous analogue vs human insulin exposure during 10 quarters for overall mortality (1.15; 95% CI, 0.97-1.34), CVD mortality (1.26; 95% CI, 0.86-1.66), MI (1.11; 95% CI, 0.77-1.45), CVA (1.30; 95% CI, 0.81-1.78), or CHF hospitalization (0.93; 95% CI, 0.75-1.11).

Conclusions and Relevance

Insulin-naive adults with type 2 diabetes who initiate and continue treatment with human vs analogue insulins had similar observed rates of major cardiovascular events, CVD mortality, and overall mortality.

Disability Transitions and Health Expectancies among Elderly People Aged 65 Years and Over in China: A Nationwide Longitudinal Study

Disability has become a critical issue among elderly populations, yet limited large-scale research related to this issue has been conducted in China, an aging society. This study explored sex and urban-rural differences in disability transitions and life expectancies among older adults in China. Data were collected from the Chinese Longitudinal Health Longevity Survey (CLHLS), which enrolled people aged 65 and older and was conducted in randomly selected counties and cities across 22 provinces in China. Disability was diagnosed based on basic activities of daily living (BADLs) and instrumental activities of daily living (IADLs). Several individual characteristics were assessed, including sociodemographic factors (age, sex and region, etc.) and health behaviors (currently smoking, currently drinking, etc.). Multistate models were applied to analyze the transition rates among 4 states: no disability, mild disability, severe disability and death. The transition rates from disabled states to the no-disability state were found to decrease markedly with age. The rates of recovery from mild disability in rural areas were higher than those in urban areas. Rural elderly individuals lived shorter lives than their urban counterparts, but they tended to live with better functional status, spending a larger fraction of their remaining life with less severe disability. Based on these findings, devoting more attention and resources to rural areas may help less severely disabled people recuperate and prevent severe disability. The study provides insights into health plan strategies to help guide the allocation of limited resources.

Dementia and Cognitive Impairment Among U.S. Veterans With a History of MDD or PTSD: A Retrospective Cohort Study Based on Sex and Race

Objective: The aim of this study was to examine major depressive disorder (MDD) and posttraumatic stress disorder (PTSD) diagnosed at age < 55 as predictors, and sex and race as potential moderators, of dementia and other forms of cognitive impairment. Method: Veterans (N = 4,800) aged ⩾ 56 years were grouped by psychiatric history, sex, and race. Hierarchical and stepwise regression were employed to determine significant predictors. Results: MDD and PTSD were associated with almost double the risk for developing dementia or cognitive impairment at age ⩾ 56. Sex, as a moderator, had small effects whereas race increased the risk almost twofold for Black veterans, given the presence of MDD history. Discussion: MDD and PTSD act as significant risk factors for dementia and other forms of cognitive impairment, and Black veterans, given a history of MDD, may be at an increased risk. An important endeavor for future research is to examine how this risk may vary across dementia subtypes and related conditions.

Socioeconomic Status, Race/Ethnicity, and Diurnal Cortisol Trajectories in Middle-Aged and Older Adults

Objectives

Slow afternoon cortisol decline may be a marker of aging. We hypothesize that lower socioeconomic status (SES) and African American race are associated with lower waking cortisol and slower afternoon decline.

Method

Six salivary cortisol samples, collected within a 24-hr period from 566 cohort participants aged 56-78 years, were examined in random-effects models. SES measures included socioeconomic vulnerability (household income and assets <500% of poverty) and education (≥college, some college, and ≤high school). African Americans were compared with all others.

Results

Adjusting for age and sex, intermediate, but not low, education was associated with approximately 17% lower average waking cortisol and 1% slower decline, compared with high education. Socioeconomic vulnerability was not associated with waking cortisol or linear decline. Accounting for African American race/ethnicity, socioeconomic vulnerability was associated with a 3% faster decline, and education was not associated with cortisol. African Americans had 26% lower average waking cortisol and 1% slower decline than others.

Discussion

African American race/ethnicity, but not lower SES, was associated with lower waking cortisol and slower afternoon decline in middle-aged and older adults. This pattern is likely a marker of earlier biological aging in vulnerable groups. Race/ethnicity may compete with SES as a measure of cumulative vulnerability.

Principles of confounder selection

Selecting an appropriate set of confounders for which to control is critical for reliable causal inference. Recent theoretical and methodological developments have helped clarify a number of principles of confounder selection. When complete knowledge of a causal diagram relating all covariates to each other is available, graphical rules can be used to make decisions about covariate control. Unfortunately, such complete knowledge is often unavailable. This paper puts forward a practical approach to confounder selection decisions when the somewhat less stringent assumption is made that knowledge is available for each covariate whether it is a cause of the exposure, and whether it is a cause of the outcome. Based on recent theoretically justified developments in the causal inference literature, the following proposal is made for covariate control decisions: control for each covariate that is a cause of the exposure, or of the outcome, or of both; exclude from this set any variable known to be an instrumental variable; and include as a covariate any proxy for an unmeasured variable that is a common cause of both the exposure and the outcome. Various principles of confounder selection are then further related to statistical covariate selection methods.

Neural correlates of domain-specific cognitive decline: The ARIC-NCS Study

OBJECTIVE

To evaluate the association of cognitive declines in the domains of memory, language, and executive function with brain gray matter (GM) volume in old age.

METHODS

This was a prospective study of 1,846 participants in the Atherosclerosis Risk in Communities (ARIC) Study who underwent 3T brain MRI scans in 2011 to 2013. Participants were categorized by cognitive domain performance trajectory over the prior 20 years (cut point to define decline: 20th percentile). Associations between GM volume and cognitive declines were assessed at the voxel level with voxel-based morphometry and at the regional level with atlas-defined GM volumes of specific regions of interest.

RESULTS

Participants were an average age of 76 years; 60% were female; and 28% were black. Participants in the top 20th percentile for decline in the memory domain had smaller GM volumes in the medial temporal lobe (-3.3%, 95% confidence interval [CI] -4.6% to -2.1%), amygdala (-2.7%, 95% CI -4.1% to -1.3%), entorhinal cortex (-4.1%, 95% CI -6.0% to -2.2%), and hippocampus (-3.8%, 95% CI -5.2% to -2.4%) compared to participants who were in the lowest 80th percentile for decline in all domains. In contrast, among participants who were in the top 20th percentile for decline in the language or executive function domains, GM volumes were smaller in more brain regions.

CONCLUSIONS

Declines in memory function were associated with brain volume loss in the medial temporal and hippocampal formations. Declines in language and executive function were associated with decreases in brain volumes across more noncontiguous brain regions.

Covariate selection strategies for causal inference: Classification and comparison

When causal effects are to be estimated from observational data, we have to adjust for confounding. A central aim of covariate selection for causal inference is therefore to determine a set that is sufficient for confounding adjustment, but other aims such as efficiency or robustness can be important as well. In this paper, we review six general approaches to covariate selection that differ in the targeted type of adjustment set. We discuss and illustrate their advantages and disadvantages using causal diagrams. Moreover, the approaches and different ways of implementing them are compared empirically in an extensive simulation study. We conclude that there are considerable differences between the approaches but none of them is uniformly best, with performance depending on the chosen adjustment method as well as the true confounding structure. Any prior structural knowledge on the causal relations is helpful to choose the most appropriate method.

Progress and future challenges in aging and diversity research in the United States

In 2016, the UC Davis Latino Aging Research Resource Center and UC Davis Alzheimer's Disease Center brought together experts from across the country to consolidate current knowledge and identify future directions in aging and diversity research. This report disseminates the research priorities that emerged from this conference, building on an earlier Gerontological Society of America preconference. We review key racial/ethnic differences in cognitive aging and dementia and identify current knowledge gaps in the field. We advocate for a systems-level framework for future research whereby environmental, sociocultural, behavioral, neuropathological, genetic, and psychometric levels of analysis are examined together to identify pathways and mechanisms that influence disparities. We then discuss steps to increase the recruitment and retention of racial/ethnic minorities in aging studies, as none of the recommendations will be possible without strong collaboration between racial/ethnic minority communities and researchers. This approach is consistent with the National Institute on Aging Health Disparities Research Framework.

Racial and Ethnic Disparities in Dementia Risk Among Individuals With Low Education

INTRODUCTION

As higher dementia prevalence in ethnic minority groups could be attributed to low education, we studied individuals with low education and explored potential factors driving dementia disparities.

METHODS

We examined differences in dementia risk between low-educated non-Hispanic whites, Hispanics, and African Americans, and the impact of lifetime risk factors using data from the nationally representative Aging, Demographics, and Memory Study (N = 819).

RESULTS

As indicated by Cox regression modeling, dementia risk of low-educated individuals was not significantly different between ethnic groups but was related to having an APOE e4 allele (hazard ratio [HR] 1.89), depression (HR 1.67), stroke (HR 1.60), and smoking (HR 1.32). Further, even in people with low education, every additional year of education decreased dementia risk (HR 0.95).

DISCUSSION

Our findings imply that higher dementia prevalence in ethnic minorities may be attributable to low education, especially among Hispanics, in addition to other risk factors.

Cognitive Aging in Black and White Americans: Cognition, Cognitive Decline, and Incidence of Alzheimer Disease Dementia

BACKGROUND

US-based studies have reported that older blacks perform worse than older whites on cognitive tests and have higher risk of Alzheimer disease dementia (AD). It is unclear whether these findings reflect differences in cognitive decline.

METHODS

The Chicago Health and Aging Project followed individuals, 65+ years old (64% black, 36% white), for up to 18 years. Participants underwent triennial cognitive assessments; stratified randomized samples underwent assessments for AD. We compared black and white participants' cognitive performance, cognitive decline rate (N = 7,735), and AD incidence (N = 2,144), adjusting for age and sex.

RESULTS

Black participants performed worse than white participants on the cognitive tests; 441 participants developed AD. Black participants' incident AD risk was twice that of whites (RR = 1.9; 95% CI, 1.4, 2.7), with 58 excess cases/1,000 occurring among blacks (95% CI, 28, 88). Among noncarriers of APOE ε4, blacks had 2.3 times the AD risk (95% CI, 1.5, 3.6), but among carriers, race was not associated with risk (RR = 1.1; 95% CI, 0.6, 2.0; Pinteraction = 0.05). However, cognitive decline was not faster among blacks: the black-white difference in 5-year change in global cognitive score was 0.007 standard unit (95% CI, -0.034, 0.047). Years of education accounted for a sizable portion of racial disparities in cognitive level and AD risk, in analyses using a counterfactual approach.

CONCLUSIONS

The higher risk of AD among blacks may stem from lower level of cognitive test performance persisting throughout the observation period rather than faster rate of late-life cognitive decline. Disparities in educational attainment may contribute to these performance disparities. See video abstract at, http://links.lww.com/EDE/B299.

High Hemoglobin A1c and Diabetes Predict Memory Decline in the Health and Retirement Study

BACKGROUND

Type 2 diabetes (T2D) is an established risk factor for dementia, but evidence for T2D and memory decline is less consistent. Understanding how T2D and blood glucose relate to memory decline is crucial to elucidating the mechanisms linking T2D and dementia.

MATERIALS AND METHODS

For 8888 Health and Retirement Study participants aged 50+, glycosylated hemoglobin (HbA1c) was measured in either 2006 or 2008 and physician's diagnosis of diabetes was self-reported in the same year. Composite memory (z scored) was assessed biennially through 2012 using immediate and delayed word list recall or the Informant Questionnaire for Cognitive Decline. Marginal mean regression models for repeated outcomes were specified to predict memory decline as a function of diabetes or HbA1c, using age as the timescale and adjusting for health and social confounders.

RESULTS

Diabetes was associated with a 10% faster rate of memory decline [β=-0.04 per decade; 95% confidence interval (CI), -0.06 to -0.01). A 1 U increase in HbA1c corresponded with a 0.05 SD decrease in memory score per decade (95% CI, -0.08 to -0.03). Even among individuals with HbA1c<6.5% (threshold for diabetes), higher HbA1c was associated with memory decline (β=-0.05 per decade; 95% CI, -0.08 to -0.03).

DISCUSSION

Diabetes accelerated memory loss and higher HbA1c predicted memory decline even in nondiabetics.

Socioeconomic, health, and psychosocial mediators of racial disparities in cognition in early, middle, and late adulthood

Racial disparities in cognitive performance exist across the life course, but it is not known whether mediators of disparities differ by age. Understanding sources of cognitive disparities at different ages can inform policies and interventions. Data were obtained for non-Hispanic Black and White respondents to The National Survey of Midlife Development in the United States from 3 age groups: 28-44 (N = 1210; 20% Black); 45-64 (N = 2693; 15% Black); and 65-85 (N = 1298; 11% Black). Moderated mediation models characterized direct and indirect effects of race on episodic memory and executive function composite scores through economic, health, and psychosocial variables as a function of age group. Education, income, chronic health conditions, and external locus of control mediated cognitive disparities across the life course, although income was a stronger mediator at younger ages. Perceived discrimination was a weaker mediator among young adults due to an absence of racial differences in perceived discrimination in that group. Despite multiple indirect effects, there were still significant unexplained effects of race on cognition that were not moderated by age group. Interventional work is needed to determine whether increasing educational attainment and income, and reducing chronic health conditions and perceived constraints among Blacks, reduce cognitive disparities. Targeting income inequality and discrimination (or buffering the impact of those variables) may be differently effective at reducing cognitive disparities at different stages of the adult life course. (PsycINFO Database Record

The Processing-Speed Impairment in Psychosis Is More Than Just Accelerated Aging

Processing speed is impaired in patients with psychosis, and deteriorates as a function of normal aging. These observations, in combination with other lines of research, suggest that psychosis may be a syndrome of accelerated aging. But do patients with psychosis perform poorly on tasks of processing speed for the same reasons as older adults? Fifty-one patients with psychotic illnesses and 90 controls with similar mean IQ (aged 19-69 years, all African American) completed a computerized processing-speed task, reminiscent of the classic digit-symbol coding task. The data were analyzed using the drift-diffusion model (DDM), and Bayesian inference was used to determine whether psychosis and aging had similar or divergent effects on the DDM parameters. Psychosis and aging were both associated with poor performance, but had divergent effects on the DDM parameters. Patients had lower information-processing efficiency ("drift rate") and longer nondecision time than controls, and psychosis per se did not influence response caution. By contrast, the primary effect of aging was to increase response caution, and had inconsistent effects on drift rate and nondecision time across patients and controls. The results reveal that psychosis and aging influenced performance in different ways, suggesting that the processing-speed impairment in psychosis is more than just accelerated aging. This study also demonstrates the potential utility of computational models and Bayesian inference for finely mapping the contributions of cognitive functions on simple neurocognitive tests.

High C-Reactive Protein Predicts Delirium Incidence, Duration, and Feature Severity After Major Noncardiac Surgery

OBJECTIVES

To examine associations between the inflammatory marker C-reactive protein (CRP) measured preoperatively and on postoperative day 2 (POD2) and delirium incidence, duration, and feature severity.

DESIGN

Prospective cohort study.

SETTING

Two academic medical centers.

PARTICIPANTS

Adults aged 70 and older undergoing major noncardiac surgery (N = 560).

MEASUREMENTS

Plasma CRP was measured using enzyme-linked immunosorbent assay. Delirium was assessed from Confusion Assessment Method (CAM) interviews and chart review. Delirium duration was measured according to number of hospital days with delirium. Delirium feature severity was defined as the sum of CAM-Severity (CAM-S) scores on all postoperative hospital days. Generalized linear models were used to examine independent associations between CRP (preoperatively and POD2 separately) and delirium incidence, duration, and feature severity; prolonged hospital length of stay (LOS, >5 days); and discharge disposition.

RESULTS

Postoperative delirium occurred in 24% of participants, 12% had 2 or more delirium days, and the mean ± standard deviation sum CAM-S was 9.3 ± 11.4. After adjusting for age, sex, surgery type, anesthesia route, medical comorbidities, and postoperative infectious complications, participants with preoperative CRP of 3 mg/L or greater had a risk of delirium that was 1.5 times as great (95% confidence interval (CI) = 1.1-2.1) as that of those with CRP less than 3 mg/L, 0.4 more delirium days (P < .001), more-severe delirium (3.6 CAM-S points higher, P < .001), and a risk of prolonged LOS that was 1.4 times as great (95% CI = 1.1-1.8). Using POD2 CRP, participants in the highest quartile (≥235.73 mg/L) were 1.5 times as likely to develop delirium (95% CI = 1.0-2.4) as those in the lowest quartile (≤127.53 mg/L), had 0.2 more delirium days (P < .05), and had more severe delirium (4.5 CAM-S points higher, P < .001).

CONCLUSION

High preoperative and POD2 CRP were independently associated with delirium incidence, duration, and feature severity. CRP may be useful to identify individuals who are at risk of developing delirium.

Survival Bias When Assessing Risk Factors for Age-Related Macular Degeneration: A Tutorial with Application to the Exposure of Smoking

PURPOSE

We illustrate the effect of survival bias when investigating risk factors for eye disease in elderly populations for whom death is a competing risk. Our investigation focuses on the relationship between smoking and late age-related macular degeneration (AMD) in an observational study impacted by censoring due to death.

METHODS

Statistical methodology to calculate the survivor average causal effect (SACE) as a sensitivity analysis is described, including example statistical computing code for Stata and R. To demonstrate this method, we examine the causal effect of smoking history at baseline (1990-1994) on the presence of late AMD at the third study wave (2003-2007) using data from the Melbourne Collaborative Cohort Study.

RESULTS

Of the 40,506 participants eligible for inclusion, 38,092 (94%) survived until the start of the third study wave, 20,752 (51%) were graded for AMD (60% female, aged 47-85 years, mean 65 ± 8.7 years). Late AMD was detected in 122 participants. Logistic regression showed strong evidence of an increased risk of late AMD for current smokers compared to non-smokers (adjusted naïve odds ratio 2.99, 95% confidence interval, CI, 1.74-5.13). Among participants expected to be alive at the start of follow-up regardless of their smoking status, the estimated SACE odds ratio comparing current smokers to non-smokers was at least 3.42 (95% CI 1.57-5.15).

CONCLUSIONS

Survival bias can attenuate associations between harmful exposures and diseases of aging. Estimation of the SACE using a sensitivity analysis approach should be considered when conducting epidemiological research within elderly populations.

Parkinson disease male-to-female ratios increase with age: French nationwide study and meta-analysis

BACKGROUND

Parkinson's disease (PD) is 1.5 times more frequent in men than women. Whether age modifies this ratio is unclear. We examined whether male-to-female (M-F) ratios change with age through a French nationwide prevalence/incidence study (2010) and a meta-analysis of incidence studies.

METHODS

We used French national drug claims databases to identify PD cases using a validated algorithm. We computed M-F prevalence/incidence ratios overall and by age using Poisson regression. Ratios were regressed on age to estimate their annual change. We identified all PD incidence studies with age/sex-specific data, and performed a meta-analysis of M-F ratios.

RESULTS

On the basis of 149 672 prevalent (50% women) and 25 438 incident (49% women) cases, age-standardised rates were higher in men (prevalence=2.865/1000; incidence=0.490/1000 person-years) than women (prevalence=1.934/1000; incidence=0.328/1000 person-years). The overall M-F ratio was 1.48 for prevalence and 1.49 for incidence. Prevalence and incidence M-F ratios increased by 0.05 and 0.14, respectively, per 10 years of age. Incidence was similar in men and women under 50 years (M-F ratio <1.2, p>0.20), and over 1.6 (p<0.001) times higher in men than women above 80 years (p trend <0.001). A meta-analysis of 22 incidence studies (14 126 cases, 46% women) confirmed that M- F ratios increased with age (0.26 per 10 years, p trend=0.005).

CONCLUSIONS

Age-increasing M-F ratios suggest that PD aetiology changes with age. Sex-related risk/protective factors may play a different role across the continuum of age at onset. This finding may inform aetiological PD research.

Neighborhood Predictors of Cognitive Training Outcomes and Trajectories in ACTIVE

We examined the influence of neighborhood socioeconomic position (SEP), racial/ethnic composition, and living in a major city on cognitive trajectories and intervention outcomes. Data came from the Advanced Cognitive Training for Independent and Vital Elderly study ( N = 2,438). Mixed effects analyses examined the associations between neighborhood variables and memory, reasoning, speed of processing, and everyday cognition, estimating differences in initial gains (potentially related to practice) and long-term rate of change over 10 years. The effect of reasoning training on initial gain was weaker for individuals in a major city. For everyday cognition, there was a stronger initial gain for memory-trained and control participants in areas with more racial/ethnic minorities and for speed-trained and control individuals in higher SEP areas. The racial/ethnic minority effect was no longer significant after adjustment for multiple comparisons. Neighborhood factors may be more important in practice-related improvement than in long-term change.

Racial Disparities in Cognitive Performance in Mid- and Late Adulthood: Analyses of Two Cohort Studies

OBJECTIVES

To examine whether the attenuation of racial disparities observed in physical health outcomes at older ages can be extended to cognitive outcomes in mid- and late-life samples.

DESIGN

Cross-sectional associations between race and cognitive functioning were examined as a function of age.

SETTING

The National Survey of Midlife Development in the United States (MIDUS) and the Washington Heights-Inwood Columbia Aging Project (WHICAP).

PARTICIPANTS

Non-Hispanic African American or white individuals aged 40 and older (MIDUS; n = 3875, 10.5% African American) and non-Hispanic African American or white individuals aged 65 and older without a diagnosis of dementia (WHICAP; n = 2,729, 53.8% African American).

MEASUREMENTS

Composite scores of executive functioning and episodic memory.

RESULTS

Independent of main effects of age, birth cohort, sex, education, and chronic health conditions, significant interactions between age and race indicated that racial disparities in episodic memory and executive functioning were larger at younger than older age in both samples.

CONCLUSION

Attenuation of racial inequalities in older age can be extended to cognitive outcomes, which probably reflects selective survival. Research on cognitive disparities or on race-specific causes of cognitive outcomes in old age must incorporate corrections for selective survival if the goal is to identify causal predictors of cognitive outcomes rather than merely statistical predictors.

Biased Exposure-Health Effect Estimates from Selection in Cohort Studies: Are Environmental Studies at Particular Risk?

BACKGROUND

The process of creating a cohort or cohort substudy may induce misleading exposure-health effect associations through collider stratification bias (i.e., selection bias) or bias due to conditioning on an intermediate. Studies of environmental risk factors may be at particular risk.

OBJECTIVES

We aimed to demonstrate how such biases of the exposure-health effect association arise and how one may mitigate them.

METHODS

We used directed acyclic graphs and the example of bone lead and mortality (all-cause, cardiovascular, and ischemic heart disease) among 835 white men in the Normative Aging Study (NAS) to illustrate potential bias related to recruitment into the NAS and the bone lead substudy. We then applied methods (adjustment, restriction, and inverse probability of attrition weighting) to mitigate these biases in analyses using Cox proportional hazards models to estimate adjusted hazard ratios (HRs) and 95% confidence intervals (CIs).

RESULTS

Analyses adjusted for age at bone lead measurement, smoking, and education among all men found HRs (95% CI) for the highest versus lowest tertile of patella lead of 1.34 (0.90, 2.00), 1.46 (0.86, 2.48), and 2.01 (0.86, 4.68) for all-cause, cardiovascular, and ischemic heart disease mortality, respectively. After applying methods to mitigate the biases, the HR (95% CI) among the 637 men analyzed were 1.86 (1.12, 3.09), 2.47 (1.23, 4.96), and 5.20 (1.61, 16.8), respectively.

CONCLUSIONS

Careful attention to the underlying structure of the observed data is critical to identifying potential biases and methods to mitigate them. Understanding factors that influence initial study participation and study loss to follow-up is critical. Recruitment of population-based samples and enrolling participants at a younger age, before the potential onset of exposure-related health effects, can help reduce these potential pitfalls.

CITATION

Weisskopf MG, Sparrow D, Hu H, Power MC. 2015. Biased exposure-health effect estimates from selection in cohort studies: are environmental studies at particular risk? Environ Health Perspect 123:1113-1122; http://dx.doi.org/10.1289/ehp.1408888.

Guidelines for reporting methodological challenges and evaluating potential bias in dementia research

Clinical and population research on dementia and related neurologic conditions, including Alzheimer's disease, faces several unique methodological challenges. Progress to identify preventive and therapeutic strategies rests on valid and rigorous analytic approaches, but the research literature reflects little consensus on "best practices." We present findings from a large scientific working group on research methods for clinical and population studies of dementia, which identified five categories of methodological challenges as follows: (1) attrition/sample selection, including selective survival; (2) measurement, including uncertainty in diagnostic criteria, measurement error in neuropsychological assessments, and practice or retest effects; (3) specification of longitudinal models when participants are followed for months, years, or even decades; (4) time-varying measurements; and (5) high-dimensional data. We explain why each challenge is important in dementia research and how it could compromise the translation of research findings into effective prevention or care strategies. We advance a checklist of potential sources of bias that should be routinely addressed when reporting dementia research.

External locus of control contributes to racial disparities in memory and reasoning training gains in ACTIVE

Racial disparities in cognitive outcomes may be partly explained by differences in locus of control. African Americans report more external locus of control than non-Hispanic Whites, and external locus of control is associated with poorer health and cognition. The aims of this study were to compare cognitive training gains between African American and non-Hispanic White participants in the Advanced Cognitive Training for Independent and Vital Elderly (ACTIVE) study and determine whether racial differences in training gains are mediated by locus of control. The sample comprised 2,062 (26% African American) adults aged 65 and older who participated in memory, reasoning, or speed training. Latent growth curve models evaluated predictors of 10-year cognitive trajectories separately by training group. Multiple group modeling examined associations between training gains and locus of control across racial groups. Compared to non-Hispanic Whites, African Americans evidenced less improvement in memory and reasoning performance after training. These effects were partially mediated by locus of control, controlling for age, sex, education, health, depression, testing site, and initial cognitive ability. African Americans reported more external locus of control, which was associated with smaller training gains. External locus of control also had a stronger negative association with reasoning training gain for African Americans than for Whites. No racial difference in training gain was identified for speed training. Future intervention research with African Americans should test whether explicitly targeting external locus of control leads to greater cognitive improvement following cognitive training.

Compared with what? An analysis of control-group types in Cochrane and Campbell reviews of psychosocial treatment efficacy with substance use disorders

BACKGROUND AND AIMS

A crucial, but under-appreciated, aspect in experimental research on psychosocial treatments of substance use disorders concerns what kinds of control groups are used. This paper examines how the distinction between different control-group designs have been handled by the Cochrane and the Campbell Collaborations in their systematic reviews of psychosocial treatments of substance abuse disorders.

METHODS

We assessed Cochrane and Campbell reviews (n = 8) that were devoted to psychosocial treatments of substance use disorders. We noted what control groups were considered and analysed the extent to which the reviews provided a rationale for chosen comparison conditions. We also analysed whether type of control group in the primary studies influenced how the reviews framed the effects discussed and whether this was related to conclusions drawn.

RESULTS

The reviews covered studies involving widely different control conditions. Overall, little attention was paid to the use of different control groups (e.g. head-to-head comparisons versus untreated controls) and what this implies when interpreting effect sizes. Seven of eight reviews did not provide a rationale for the choice of comparison conditions.

CONCLUSIONS

Cochrane and Campbell reviews of the efficacy of psychosocial interventions with substance use disorders seem to underappreciate that the use of different control-group types yields different effect estimates. Most reviews have not distinguished between different control-group designs and therefore have provided a confused picture regarding absolute and relative treatment efficacy. A systematic approach to treating different control-group designs in research reviews is necessary for meaningful estimates of treatment efficacy.

Hippocampal atrophy and subsequent depressive symptoms in older men and women: results from a 10-year prospective cohort

Several studies have reported smaller hippocampal volume in patients with depression. However, the temporality of the association is undetermined. One hypothesis is that hippocampal atrophy might be a susceptibility factor for depression. In the present study, we assessed whether hippocampal atrophy was associated with subsequent depressive symptoms in a cohort of older French adults (n = 1,309) who were 65-80 years of age and enrolled into the study in 1999-2001 in Dijon, France. Subjects were followed for more than 10 years. Participants underwent 2 cerebral magnetic resonance imaging scans, one at baseline and one at the 4-year follow-up. We used linear mixed models to estimate the associations of hippocampal atrophy with 1) the average depressive symptom scores over follow-up (using the Center for Epidemiologic Studies-Depression scale) measured biennially over the subsequent 6 years and 2) changes in symptom scores over follow-up. In women, a 2-standard-deviation increase in annual hippocampal atrophy was associated with a 1.67-point (95% confidence interval: 0.59, 2.77) increase in the average depressive symptom score over follow-up and with a 1.97-point (95% confidence interval: 0.68, 3.24) increase in scores over the 2 subsequent years but not with later changes in symptoms. No association was detected in men. Accounting for potential selective attrition (using inverse probability weights) did not alter results. Hippocampal atrophy was associated with more subsequent depressive symptoms and with shorter-term worsening of symptoms in women.

A review of covariate selection for non-experimental comparative effectiveness research

This paper addresses strategies for selecting variables for adjustment in non-experimental comparative effectiveness research and uses causal graphs to illustrate the causal network that relates treatment to outcome. Variables in the causal network take on multiple structural forms. Adjustment for a common cause pathway between treatment and outcome can remove confounding, whereas adjustment for other structural types may increase bias. For this reason, variable selection would ideally be based on an understanding of the causal network; however, the true causal network is rarely known. Therefore, we describe more practical variable selection approaches based on background knowledge when the causal structure is only partially known. These approaches include adjustment for all observed pretreatment variables thought to have some connection to the outcome, all known risk factors for the outcome, and all direct causes of the treatment or the outcome. Empirical approaches, such as forward and backward selection and automatic high-dimensional proxy adjustment, are also discussed. As there is a continuum between knowing and not knowing the causal, structural relations of variables, we recommend addressing variable selection in a practical way that involves a combination of background knowledge and empirical selection and that uses high-dimensional approaches. This empirical approach can be used to select from a set of a priori variables based on the researcher's knowledge to be included in the final analysis or to identify additional variables for consideration. This more limited use of empirically derived variables may reduce confounding while simultaneously reducing the risk of including variables that may increase bias.

Lifestyle, social factors, and survival after age 75: population based study

OBJECTIVE

To identify modifiable factors associated with longevity among adults aged 75 and older.

DESIGN

Population based cohort study.

SETTING

Kungsholmen, Stockholm, Sweden.

PARTICIPANTS

1810 adults aged 75 or more participating in the Kungsholmen Project, with follow-up for 18 years.

MAIN OUTCOME MEASURE

Median age at death. Vital status from 1987 to 2005.

RESULTS

During follow-up 1661 (91.8%) participants died. Half of the participants lived longer than 90 years. Half of the current smokers died 1.0 year (95% confidence interval 0.0 to 1.9 years) earlier than non-smokers. Of the leisure activities, physical activity was most strongly associated with survival; the median age at death of participants who regularly swam, walked, or did gymnastics was 2.0 years (0.7 to 3.3 years) greater than those who did not. The median survival of people with a low risk profile (healthy lifestyle behaviours, participation in at least one leisure activity, and a rich or moderate social network) was 5.4 years longer than those with a high risk profile (unhealthy lifestyle behaviours, no participation in leisure activities, and a limited or poor social network). Even among the oldest old (85 years or older) and people with chronic conditions, the median age at death was four years higher for those with a low risk profile compared with those with a high risk profile.

CONCLUSION

Even after age 75 lifestyle behaviours such as not smoking and physical activity are associated with longer survival. A low risk profile can add five years to women's lives and six years to men's. These associations, although attenuated, were also present among the oldest old (≥ 85 years) and in people with chronic conditions.

Is cognitive aging predicted by one's own or one's parents' educational level? results from the three-city study

The authors examined the associations of participants' and their parents' educational levels with cognitive decline while addressing methodological limitations that might explain inconsistent results in prior work. Residents of Dijon, France (n = 4,480) 65 years of age or older who were enrolled between 1999 and 2001 were assessed using the Isaacs' verbal fluency test, Benton Visual Retention Test, Trail Making Test B, and Mini-Mental State Examination up to 5 times over 9 years. The authors used random-intercepts mixed models with inverse probability weighting to account for differential survival (conditional on past performance) and quantile regressions to assess bias from measurement floors or ceilings. Higher parental educational levels predicted better average baseline performances for all tests but a faster average decline in score on the Isaacs' test. Higher participant educational attainment predicted better baseline performances on all tests and slower average declines in Benton Visual Retention Test, Trail Making Test B, and Mini-Mental State Examination scores. Slope differences were generally small, and most were not robust to alternative model specifications. Quantile regressions suggested that ceiling effects might have modestly biased effect estimates, although the direction of this bias might depend on the test instrument. These findings suggest that the possible impacts of educational experiences on cognitive change are small, domain-specific, and potentially incorrectly estimated in conventional analyses because of measurement ceilings.