Impact of missing data mechanism on the estimate of change: a case study on cognitive function and polypharmacy among older persons

Modeling of correlated cognitive function and functional disability outcomes with bounded and missing data in a longitudinal aging study

Longitudinal studies of correlated cognitive and disability outcomes among older adults are characterized by missing data due to death or loss to follow-up from deteriorating health conditions. The Mini-Mental State Examination (MMSE) score for assessing cognitive function ranges from a minimum of 0 (floor) to a maximum of 30 (ceiling). To study the risk factors of cognitive function and functional disability, we propose a shared parameter model to handle missingness, correlation between outcomes, and the floor and ceiling effects of the MMSE measurements. The shared random effects in the proposed model handle missingness (either missing at random or missing not at random) and correlation between these outcomes, while the Tobit distribution handles the floor and ceiling effects of the MMSE measurements. We used data from the Chinese Longitudinal Healthy Longevity Survey (CLHLS) and a simulation study. By ignoring the MMSE floor and ceiling effects in the analyses of the CLHLS, the association of systolic blood pressure with cognitive function was not significant and the association of age with cognitive function was lower by 16.6% (from -6.237 to -5.201). By ignoring the MMSE floor and ceiling effects in the simulation study, the relative bias in the estimated association of female gender with cognitive function was 43 times higher (from -0.01 to -0.44). The estimated associations obtained with data missing at random were smaller than those with data missing not at random, demonstrating how the missing data mechanism affects the analytic results. Our work underscores the importance of proper model specification in longitudinal analysis of correlated outcomes subject to missingness and bounded values.

Are there gender differences in the trajectories of self-rated health among chinese older adults? an analysis of the Chinese Longitudinal Healthy Longevity Survey (CLHLS)

BACKGROUND

Self-rated health (SRH) is a good predictor of morbidity and mortality. Extensive research has shown that females generally report poorer SRH than males but still tend to live longer. Previous studies used cross-sectional or pooled data for their analyses while ignoring the dynamic changes in males' and females' SRH statuses over time. Furthermore, longitudinal studies, especially those that focus on older adults, typically suffer from the incompleteness of data. As such, the effect of dropout data on the trajectories of SRH is still unknown. Our objective is to examine whether there are any gender differences in the trajectories of SRH statuses in Chinese older adults.

METHODS

The trajectories of SRH were estimated using the pattern-mixture model (PMM), a special latent growth model, under non-ignorable dropout data assumption. We analyzed the Chinese Longitudinal Healthy Longevity Survey (CLHLS) data of 15,613 older adults aged 65 years and above, collected from 2005 to 2014.

RESULTS

The results demonstrated the effect of non-ignorable dropout data assumptions in this study. The previous SRH score was negatively associated with the likelihood of dropping out of the study at the next follow-up survey. Our results showed that both males and females in China perceive their SRH as decreasing over time. A significant gender difference was found in the average SRH score (female SRH was lower than male SRH) in this study. Nonetheless, based on the results obtained using the PMM, there are no gender differences in the trajectories of SRH at baseline as well as in the rate of decline among the total sample. The results also show that males and females respond to SRH predictors similarly, except that current drinking has a more pronounced positive effect on males and healthcare accessibility has a more pronounced positive effect on females.

CONCLUSIONS

Our results suggest that missing data have an impact on the trajectory of SRH among Chinese older adults. Under the non-ignorable dropout data assumptions, no gender differences were found in trajectories of SRH among Chinese older adults. Males and females respond to SRH predictors similarly, except for current drinking habit and healthcare accessibility.

Longitudinal associations between different dementia diagnoses and medication use jointly accounting for dropout

ABSTRACTBackground:Longitudinal studies of older adults are characterized by high dropout rates, multimorbid conditions, and multiple medication use, especially proximal to death. We studied the association between multiple medication use and incident dementia diagnoses including Alzheimer's disease (AD), vascular dementia (VD), and Lewy-body dementia (LBD), simultaneously accounting for dropout.

METHODS

Using the National Alzheimer's Coordinating Center data with three years of follow-up, a set of covariate-adjusted models that ignore dropout was fit to complete-case data, and to the whole-cohort data. Additionally, covariate-adjusted joint models with shared random effects accounting for dropout were fit to the whole-cohort data. Multiple medication use was defined as polypharmacy (⩾ five medications), hyperpolypharmacy (⩾ ten medications), and total number of medications.

RESULTS

Incident diagnoses were 2,032 for AD, 135 for VD, and 139 for LBD. Percentages of dropout at the end of follow-up were as follows: 71.8% for AD, 81.5% for VD, and 77.7% for LBD. The odds ratio (OR) estimate for hyperpolypharmacy among those with LBD versus AD was 2.19 (0.78, 6.15) when estimated using complete-case data and 3.00 (1.66, 5.40) using whole-cohort data. The OR reduced to 1.41 (0.76, 2.64) when estimated from the joint model accounting for dropout. The OR for polypharmacy using complete-case data differed from the estimates using whole-cohort data. The OR for dementia diagnoses on total number of medications was similar, but non-significant when estimated using complete-case data.

CONCLUSION

Reasons for dropout should be investigated and appropriate statistical methods should be applied to reduce bias in longitudinal studies among high-risk dementia cohorts.

Changes in Drug Use and Polypharmacy After the Age of 90: A Longitudinal Study of the Danish 1905 Cohort

OBJECTIVES

To determine the longitudinal development of drug use in very old adults.

DESIGN

Longitudinal cohort study with waves in 1998, 2000, 2002, and 2005.

SETTING

Nationwide study in Denmark.

PARTICIPANTS

All living Danes born in 1905 were approached in 1998; 2,262 responded at baseline.

MEASUREMENTS

Self-reported use of regularly taken drugs. Mean and median number of drugs and growth curve models were used to identify the change in number of drugs as the cohort aged from 92 to 100.

RESULTS

The within-person use of drugs increased with age for women (0.19 per year; 95% confidence interval (CI) = 0.15-0.24) and men (0.15 per year; 95% CI = 0.06-0.24). Persons leaving the study prematurely had higher baseline values and a steeper increase in their annual use of drugs. The population-level mean number of drugs increased from baseline (3.6 drugs) to the first follow-up (4.1 drugs) but thereafter remained stable at approximately 4 drugs. Women used more drugs than men at all waves.

CONCLUSION

In this first longitudinal study of drug use in nonagenarians, individuals used an increasing number of drugs as they aged. This increase is difficult to detect in cross-sectional analyses of the population-level mean. More efforts to understand what is reasonable prescribing at these older ages are needed.

Factors related to the evolution of Health Related Quality of Life in coronary patients. A longitudinal approach using Weighted Generalized Estimating Equations with missing data

BACKGROUND

The aim is to know the factors related to the evolution of Health Related Quality of Life (HRQL) in Coronary Patients (CP) from a longitudinal perspective using an appropriate method that handles missing data adequately when the mechanism of missingness is uncertain.

METHODS

Prospective study with repeated measures at baseline, 3 and 6months. 250 patients with acute myocardial infarction or unstable angina were studied. Sociodemographic and clinical data were collected at baseline. Mental health (GHQ-28) and HRQL (SF-36v1) were assessed during the follow-up. The missingness mechanism was tested. Friedman test and partial eta-squared were used to analyse changes in SF-36 scores and WGEE were used to identify the predictors of the evolution of HRQL.

RESULTS

95 dropped out after 3months and 72 after 6months. The missingness was likely to be at random. All the dimensions of the SF-36 improved over time, except PF. The factors related to the evolution of HRQL were: being woman (B=-23.9 in RE; B=-6.9 in MCS), older age (B=-0.5 in BP; B=-0.3 in VT), being single/separated (B=-14.5 in GH; B=-14.1 in SF; B=-23.3 in MH) and widow(er) (B=-23.2 PF; B=-29.8 in SF), hypertensive (B=-19.8 in RP; B=-8.9 in VT), worse mental health (B=-3 in PF; B=-2.8 in RP; B=-3.1 in BP; B=-1.2 in PCS; B=-3.8 in VT; B=-2.6 in SF), previous history of CHD (B=-12.5 in PF; B=-5.2 in PCS), and performing heart-healthy physical activities (B=13.9 in PF).

CONCLUSIONS

HRQL improves over time. A global approach, including age, marital status, performing physical activities or hypertension, is required to improve HRQL in CP.