What Is the Causal Interpretation of Sibling Comparison Designs?

Antiseizure medication use during pregnancy and children's neurodevelopmental outcomes

The teratogenic potential of valproate in pregnancy is well established; however, evidence regarding the long-term safety of other antiseizure medications (ASMs) during pregnancy remains limited. Using routinely collected primary care data from the UK and nationwide Swedish registries to create a cohort of 3,182,773 children, of which 17,495 were exposed to ASMs in pregnancy, we show that those exposed to valproate were more likely to receive a diagnosis of autism, intellectual disability, and ADHD, when compared to children not exposed to ASMs. Additionally, children exposed to topiramate were 2.5 times more likely to be diagnosed with intellectual disability (95% CI: 1.23-4.98), and those exposed to carbamazepine were 1.25 times more likely to be diagnosed with autism (95% CI: 1.05-1.48) and 1.30 times more likely to be diagnosed with intellectual disability (95% CI: 1.01-1.69). There was little evidence that children exposed to lamotrigine in pregnancy were more likely to receive neurodevelopmental diagnoses. While further research is needed, these findings may support considering safer treatment alternatives well before conception when clinically appropriate.

Neighborhood mobility and racial disparities in preterm birth: A sibling study in California

Recent work finds that upward neighborhood mobility-defined as reductions in neighborhood socioeconomic disadvantage due to moving-may improve birth outcomes. Less work, however, explores whether changes in socioeconomic context differentially impact birth outcomes by maternal race and ethnicity. In the US, mothers of minoritized racial and ethnic identity often experience worse neighborhood conditions and pregnancy outcomes than White mothers. Using a sibling-linked dataset, we examined whether neighborhood mobility corresponds with changes in preterm birth risk among Asian (N = 130,079), Black (N = 50,149), Hispanic (N = 429,938), and White (N = 233,428) mothers who delivered multiple live births in California between 2005 and 2015. We linked residential addresses at each birth to census-derived indices of neighborhood disadvantage and defined levels of neighborhood mobility as moving-induced changes in disadvantage between pregnancies. We mapped neighborhood mobility patterns and fit conditional logistic regression models estimating the odds of preterm birth in the sibling delivered after moving, controlling for the risk of preterm birth in the sibling delivered before moving, by maternal race and ethnicity. Dot density maps highlight racialized patterns of neighborhood mobility and segregation between Black and White mothers. Regression results show that Black and, in some cases, Asian and Hispanic mothers who experienced upward mobility (moves away from neighborhood disadvantage) exhibited reduced odds of preterm birth in the second delivery. Upward mobility did not reduce the odds of preterm birth among White mothers. Findings suggest that policies and programs that enable opportunities for neighborhood mobility may reduce persistent racial and ethnic disparities in adverse birth outcomes.

First-trimester use of antiseizure medications and the risk of miscarriage: a population-based cohort study

BACKGROUND

Antiseizure medications (ASMs) during the first trimester of pregnancy have been associated with an increased risk of miscarriage.

METHODS

We carried out a population-based cohort study using routinely collected healthcare data from the UK, 1995-2018. Pregnancies were identified in the Clinical Practice Research Datalink and we estimated the HR of miscarriage associated with prescriptions of ASMs during the first trimester of pregnancy, using Cox regression, adjusting for potential confounders, including ASM indications.

RESULTS

ASMs were prescribed during the first trimester in 7832 (0.8%) of 1 023 787 included pregnancies. 14.5% of pregnancies with first-trimester exposure to ASMs ended in miscarriage, while 12.2% without ASM exposure in the first trimester ended in miscarriage; after adjustment, there was a 1.06-fold relative hazard of miscarriage (95% CI 1.00 to 1.13) in women with first-trimester ASM use. After restricting to women with specific ASM indications, this association was not evident in women with epilepsy (adjusted HR 0.98, 95% CI 0.89 to 1.08), but was observed in women with bipolar or other psychiatric conditions (1.08, 95% CI 1.00 to 1.16) although CIs overlapped. Compared with discontinuation of ASMs prior to pregnancy, there was no evidence of increased risk of miscarriage for first-trimester ASM use in women with bipolar or other psychiatric conditions (1.02, 95% CI 0.87 to 1.20).

CONCLUSION

We found no clear evidence to suggest that first-trimester ASM use increased the risk of miscarriage. Taken together, our analyses suggest that apparent associations between first-trimester ASM use and miscarriage may be the result of confounding by the presence of a bipolar disorder or associated unmeasured variables.

Accelerated biological aging six decades after prenatal famine exposure

To test the hypothesis that early-life adversity accelerates the pace of biological aging, we analyzed data from the Dutch Hunger Winter Families Study (DHWFS, N = 951). DHWFS is a natural-experiment birth-cohort study of survivors of in-utero exposure to famine conditions caused by the German occupation of the Western Netherlands in Winter 1944 to 1945, matched controls, and their siblings. We conducted DNA methylation analysis of blood samples collected when the survivors were aged 58 to quantify biological aging using the DunedinPACE, GrimAge, and PhenoAge epigenetic clocks. Famine survivors had faster DunedinPACE, as compared with controls. This effect was strongest among women. Results were similar for GrimAge, although effect-sizes were smaller. We observed no differences in PhenoAge between survivors and controls. Famine effects were not accounted for by blood-cell composition and were similar for individuals exposed early and later in gestation. Findings suggest in-utero undernutrition may accelerate biological aging in later life.

Disentangling potential causal effects of educational duration on well-being, and mental and physical health outcomes

BACKGROUND

Extensive research has focused on the potential benefits of education on various mental and physical health outcomes. However, whether the associations reflect a causal effect is harder to establish.

METHODS

To examine associations between educational duration and specific aspects of well-being, anxiety and mood disorders, and cardiovascular health in a sample of European Ancestry UK Biobank participants born in England and Wales, we apply four different causal inference methods (a natural policy experiment leveraging the minimum school-leaving age, a sibling-control design, Mendelian randomization [MR], and within-family MR), and assess if the methods converge on the same conclusion.

RESULTS

A comparison of results across the four methods reveals that associations between educational duration and these outcomes appears predominantly to be the result of confounding or bias rather than a true causal effect of education on well-being and health outcomes. Although we do consistently find no associations between educational duration and happiness, family satisfaction, work satisfaction, meaning in life, anxiety, and bipolar disorder, we do not find consistent significant associations across all methods for the other phenotypes (health satisfaction, depression, financial satisfaction, friendship satisfaction, neuroticism, and cardiovascular outcomes).

CONCLUSIONS

We discuss inconsistencies in results across methods considering their respective limitations and biases, and additionally discuss the generalizability of our findings in light of the sample and phenotype limitations. Overall, this study strengthens the idea that triangulation across different methods is necessary to enhance our understanding of the causal consequences of educational duration.

Estimating a Theoretically Consistent Human Capital Production Function With an Application to Head Start

This article describes a conceptual and empirical approach for estimating a human capital production function of child development that incorporates mother- or child-fixed effects. The use of mother- or child-fixed effects is common in this applied economics literature, but its application is often inconsistent with human capital theory. We outline the problem and demonstrate its empirical importance with an analysis of the effect of Head Start and preschool on child and adult outcomes. The empirical specification we develop has broad implications for a variety of applied microeconomic analyses beyond our specific application. Results of our analysis indicate that attending Head Start or preschool had no economically or statistically significant effect on child or adult outcomes.

Educational Mobility, Pace of Aging, and Lifespan Among Participants in the Framingham Heart Study

Importance

People who complete more education live longer lives with better health. New evidence suggests that these benefits operate through a slowed pace of biological aging. If so, measurements of the pace of biological aging could offer intermediate end points for studies of how interventions to promote education will affect healthy longevity.

Objective

To test the hypothesis that upward educational mobility is associated with a slower pace of biological aging and increased longevity.

Design, Setting, and Participants

This prospective cohort study analyzed data from 3 generations of participants in the Framingham Heart Study: (1) the original cohort, enrolled beginning in 1948; (2) the Offspring cohort, enrolled beginning in 1971; and (3) the Gen3 cohort, enrolled beginning in 2002. A 3-generation database was constructed to quantify intergenerational educational mobility. Mobility data were linked with blood DNA-methylation data collected from the Offspring cohort in 2005 to 2008 (n = 1652) and the Gen3 cohort in 2009 to 2011 (n = 1449). Follow-up is ongoing. Data analysis was conducted from June 2022 to November 2023 using data obtained from the National Institutes of Health database of Genotypes and Phenotypes (dbGaP).

Exposure

Educational mobility was measured by comparing participants' educational outcomes with those of their parents.

Main Outcomes and Measures

The pace of biological aging was measured from whole-blood DNA-methylation data using the DunedinPACE epigenetic clock. For comparison purposes, the analysis was repeated using 4 other epigenetic clocks. Survival follow-up was conducted through 2019.

Results

This study analyzed data from 3101 participants from the Framingham Heart Study; 1652 were in the Offspring cohort (mean [SD] age, 65.57 [9.22] years; 764 [46.2%] male) and 1449 were in the Gen3 cohort (mean [SD] age, 45.38 [7.83] years; 691 [47.7%] male). Participants who were upwardly mobile in educational terms tended to have slower pace of aging in later life (r = -0.18 [95% CI, -0.23 to -0.13]; P < .001). This pattern of association was similar across generations and held in within-family sibling comparisons. There were 402 Offspring cohort participants who died over the follow-up period. Upward educational mobility was associated with lower mortality risk (hazard ratio, 0.89 [95% CI, 0.81 to 0.98]; P = .01). Slower pace of aging accounted for approximately half of this association.

Conclusions and Relevance

This cohort study's findings support the hypothesis that interventions to promote educational attainment may slow the pace of biological aging and promote longevity. Epigenetic clocks have potential as near-term outcome measures of intervention effects on healthy aging. Experimental evidence is needed to confirm findings.

Low and very low birthweight disadvantage in compulsory education achievement and the transition to upper secondary education in the Finnish birth cohorts of 1987 to 1997

BACKGROUND

We compared the educational achievements of very low-birthweight (VLBW) and low-birthweight (LBW) adolescents (ages 16 to 19) to those of their normal-birthweight (NBW) peers in the complete Finnish birth cohorts of 1987 to 1997. We focused on three key phases of the education process: the end of compulsory education (9th-grade completion), and the transition to and the completion of upper secondary-level education.

METHODS

We used register data on grades, educational transitions and completed education. We employed multiple indicators on the progression of the education process and estimated population-level and within-families linear probability (LPM) models with robustness checks at the population level using logistic regression. We tested whether parental education and the child's sex modify the association between (V)LBW and educational achievement.

RESULTS

Results of both descriptive analysis and the population-level and within-family LPM models indicate that (V)LBW is associated with an increased risk of not being able to keep up with the normative education process and to compete for upper secondary education study places at the end of compulsory education. The modifying effect of parental education was robust, whereas that of the child's sex was not. Among (V)LBW students who were able to keep up with the normative education process, (V)LBW was not associated with a lower grade point average or with a meaningfully lower probability of completing upper secondary education by the normative age.

CONCLUSIONS

The upper secondary-level educational choices and achievements of the children born with (V)LBW who managed to complete the standard compulsory education curriculum and complete the transition to upper secondary-level education within the expected time did not, in essence, differ from those of the NBW children. Some specific characteristics of the Finnish education system likely contributed to these results, such as the grading at compulsory education being only relatively loosely standardized.

Understanding the impact of non-shared unmeasured confounding on the sibling comparison analysis

BACKGROUND

The sibling comparison analysis is used to deal with unmeasured confounding. It has previously been shown that in the presence of non-shared unmeasured confounding, the sibling comparison analysis may introduce substantial bias depending on the sharedness of the unmeasured confounder and the sharedness of the exposure. We aimed to improve the awareness of this challenge of the sibling comparison analysis.

METHODS

First, we simulated sibling pairs with an exposure, a confounder and an outcome. We simulated sibling pairs with no effect of the exposure on the outcome and with positive confounding. For varying degrees of sharedness of the confounder and the exposure and for varying prevalence of the exposure, we calculated the sibling comparison odds ratio (OR). Second, we provided measures for sharedness of selected treatments based on Danish health data.

RESULTS

The confounded sibling comparison OR was visualized for varying degrees of sharedness of the confounder and the exposure and for varying prevalence of the exposure. The confounded sibling comparison OR was seen to increase with increasing sharedness of the exposure and the confounded sibling comparison OR decreased with an increasing prevalence of exposure. Measures for sharedness of treatments based on Danish health data showed that treatments of chronic diseases have the highest sharedness and treatments of non-chronic diseases have the lowest sharedness.

CONCLUSIONS

Researchers should be aware of the challenge regarding non-shared unmeasured confounding in the sibling comparison analysis, before applying the analysis in non-randomized studies. Otherwise, the sibling comparison analysis may lead to substantial bias.

Accelerated biological aging six decades after prenatal famine exposure

To test the hypothesis that early-life adversity accelerates the pace of biological aging, we analyzed data from the Dutch Hunger Winter Families Study (DHWFS, N=951). DHWFS is a natural-experiment birth-cohort study of survivors of in-utero exposure to famine conditions caused by the German occupation of the Western Netherlands in Winter 1944-5, matched controls, and their siblings. We conducted DNA methylation analysis of blood samples collected when the survivors were aged 58 to quantify biological aging using the DunedinPACE, GrimAge, and PhenoAge epigenetic clocks. Famine survivors had faster DunedinPACE, as compared with controls. This effect was strongest among women. Results were similar for GrimAge, although effect-sizes were smaller. We observed no differences in PhenoAge between survivors and controls. Famine effects were not accounted for by blood-cell composition and were similar for individuals exposed early and later in gestation. Findings suggest in-utero undernutrition may accelerate biological aging in later life.

Estimating the Influence of Adolescents' Non-Cognitive Skills on Awareness of Social Disaster Responses

BACKGROUND

This study examines the influence of 2 noncognitive skills, self-esteem and teamwork, on social disaster response awareness among Korean adolescents. Although self-esteem is a well-established predictor of health-related knowledge, the inclusion of teamwork in this study is motivated by its collective nature and its relevance to social norms.

METHODS

This study used data from the Korean Children and Youth Panel Survey 2018 (KCYPS 2018). Sibling fixed effects models, which account for the common unobserved characteristics shared by siblings within the same family, were estimated.

RESULTS

Conventional ordinary least square models showed that both self-esteem and teamwork are significant predictors of social disaster response awareness (bs = .011 and .014, respectively). However, our preferred sibling fixed effects estimates revealed that the controlling for unobserved family-level confounders attenuates the association for self-esteem, rendering it statistically insignificant (b = .003, p = .33). Despite some attenuation, the association between teamwork and social disaster response awareness was robust to controlling for sibling fixed effects (b = .010, p < .001).

CONCLUSIONS

The study's finding emphasizes the role of students' interpersonal noncognitive abilities in their social disaster response awareness. An intervention aimed at enhancing adolescents' teamwork may be effective to improve their awareness about how to respond to social disasters. Policymakers and practitioners may consider developing social disaster preparedness curricula that highlight the importance of social disaster response measures as community rules or social norms, in addition to safeguarding personal safety.

Differential exposure to gun or knife violence over two decades is associated with sibling differences in depression

We tested whether exposure to gun or knife violence over two decades is a cause of depression in young adulthood using data from a nationally representative sample in the United States. The National Longitudinal Study of Adolescent to Adult Health is a sample of 20,745 adolescents, assessed in 1994-95 with follow-ups in 1995-1996 (n = 14,738), 2001-2002 (n = 15,197) and 2007-2008 (n = 15,701; 24 to 32 years old). At each wave, respondents reported exposure to gun or knife violence and symptoms of depression. Regression and sibling fixed effects analyses were conducted to test whether cumulative exposure to gun or knife violence was associated with depression. In fully adjusted models, greater cumulative exposure to gun or knife violence was associated with more symptoms of depression (b = 0.12, 95% C. I. = 0.05; 0.19, p < 0.01) and higher risk for clinically significant depression in young adulthood (OR = 1.07, 95% C. I. = 1.02; 1.13, p < 0.01). Results replicated in sibling fixed effects models (b = 0.21, 95% C. I. = 0.01; 0.42, p < 0.05). These quasi-experimental data suggest that exposure to gun or knife violence is a cause of depression in young adulthood.

Association of caesarean delivery with offspring health outcomes in full-cohort versus sibling-comparison studies: a comparative meta-analysis and simulation study

BACKGROUND

Full-cohort and sibling-comparison designs have yielded inconsistent results about the impacts of caesarean delivery on offspring health outcomes, with the effect estimates from the latter being more likely directed towards the null value. We hypothesized that the seemingly conservative results obtained from the sibling-comparison design might be attributed to inadequate adjustment for non-shared confounders between siblings, particularly maternal age at delivery.

METHODS

A systematic review and meta-analysis was first conducted. PubMed, Embase, and the Web of Science were searched from database inception to April 6, 2022. Included studies (1) examined the association of caesarean delivery, whether elective or emergency, with offspring health outcomes; (2) simultaneously conducted full-cohort and sibling-comparison analyses; and (3) reported adjusted effect estimates with 95% confidence intervals (95% CIs). No language restrictions were applied. Data were extracted by 2 reviewers independently. Three-level meta-analytic models were used to calculate the pooled odds ratios (ORs) and 95% CIs for caesarean versus vaginal delivery on multiple offspring health outcomes separately for full-cohort and sibling-comparison designs. Subgroup analyses were performed based on the method of adjustment for maternal age at delivery. A simulation study was then conducted. The simulated datasets were generated with some key parameters derived from the meta-analysis.

RESULTS

Eighteen studies involving 21,854,828 individuals were included. The outcomes assessed included mental and behavioral disorders; endocrine, nutritional and metabolic diseases; asthma; cardiorespiratory fitness; and multiple sclerosis. The overall pooled OR for estimates from the full-cohort design was 1.14 (95% CI: 1.11 to 1.17), higher than that for estimates from the sibling-comparison design (OR = 1.08; 95% CI: 1.02 to 1.14). Stratified analyses showed that estimates from the sibling-comparison design varied considerably across studies using different methods to adjust for maternal age at delivery in multivariate analyses, while those from the full-cohort design were rather stable: in studies that did not adjust maternal age at delivery, the pooled OR of full-cohort vs. sibling-comparison design was 1.10 (95% CI: 0.99 to 1.22) vs. 1.06 (95% CI: 0.85 to 1.31), in studies adjusting it as a categorical variable, 1.15 (95% CI: 1.11 to 1.19) vs. 1.07 (95% CI: 1.00 to 1.15), and in studies adjusting it as a continuous variable, 1.12 (95% CI: 1.05 to 1.19) vs. 1.12 (95% CI: 0.98 to 1.29). The severe underestimation bias related to the inadequate adjustment of maternal age at delivery in sibling-comparison analyses was fully replicated in the simulation study.

CONCLUSIONS

Sibling-comparison analyses may underestimate the association of caesarean delivery with multiple offspring health outcomes due to inadequate adjustment of non-shared confounders, such as maternal age at delivery. Thus, we should be cautious when interpreting the seemingly conservative results of sibling-comparison analyses in delivery-related studies.

The association between parental internalizing disorders and child school performance

Parents play a crucial role in children's lives. Despite high prevalences of anxiety and depression, we do not know how these disorders among parents associate with child school performance in Norway. We use regression models to estimate associations between parental mental disorders and child school performance, while adjusting for some social and genetic confounders. Parental anxiety and depression were assessed from administrative registers of government funded health service consultations for all individuals in Norway with children born between 1992 and 2002. School performance was assessed as standardized grade point average at the end of compulsory education when children are 16 years old. Associations were also considered in samples of adoptees and among differentially affected siblings. We find that 18.8% of children have a parent with an anxiety or depression diagnosis from primary care during the last three years of compulsory education (yearly prevalence: 11.5%). There is a negative association between these parental mental disorders and child school outcomes (z = 0.43). This association was weakened, but statistically significant among differentially exposed siblings (z = 0.04), while disappearing in adoptee children. Many children experience that their parents have anxiety or depression and receive a diagnosis from primary care. On average, these children have lower school performance. The association is attenuated when comparing differentially exposed siblings and disappears in adoptee children. These results have a poor fit with the hypothesis that parental internalizing is an influential causal factor in determining children's educational success.

Annual Research Review: Towards a deeper understanding of nature and nurture: combining family-based quasi-experimental methods with genomic data

Distinguishing between the effects of nature and nurture constitutes a major research goal for those interested in understanding human development. It is known, for example, that many parent traits predict mental health outcomes in children, but the causal processes underlying such associations are often unclear. Family-based quasi-experimental designs such as sibling comparison, adoption and extended family studies have been used for decades to distinguish the genetic transmission of risk from the environmental effects family members potentially have on one another. Recently, these designs have been combined with genomic data, and this combination is fuelling a range of exciting methodological advances. In this review we explore these advances - highlighting the ways in which they have been applied to date and considering what they are likely to teach us in the coming years about the aetiology and intergenerational transmission of psychopathology.

In utero exposure to ADHD medication and long-term offspring outcomes

Attention Deficit Hyperactivity Disorder (ADHD) medication is increasingly being used during pregnancy. Concerns have been raised as to whether ADHD medication has long-term adverse effects on the offspring. The authors investigated whether in utero exposure to ADHD medication was associated with adverse long-term neurodevelopmental and growth outcomes in offspring. The population-based cohort study in the Danish national registers included 1,068,073 liveborn singletons from 1998 to 2015 followed until any developmental diagnosis, death, emigration, or December 31, 2018. Children of mothers who continued ADHD medication (methylphenidate, amphetamine, dexamphetamine, lisdexamphetamine, modafinil, atomoxetine, clonidine) during pregnancy and children of mothers who discontinued ADHD medication before pregnancy were compared using Cox regression. Main outcomes were neurodevelopmental psychiatric disorders, impairments in vision or hearing, epilepsy, seizures, or growth impairment during childhood or adolescence. In total, 898 children were exposed to ADHD medication during pregnancy compared to 1270 children whose mothers discontinued ADHD medication before pregnancy. After adjustment for demographic and psychiatric characteristics of the mother, no increased risk of any offspring developmental disorders was found combined (aHR 0.97, 95% CI 0.81 to 1.17) or for separate subcategories. Similarly, no increased risk was found for any sub-categories of outcomes in the negative control or sibling controlled analyses. Neurodevelopment and growth in offspring do not differ based on antenatal exposure to ADHD medication. These findings provide reassurance for women with ADHD who depend on ADHD medication for daily functioning and who consider continuing medication in pregnancy.

The mobility effects hypothesis: Methods and applications

We discuss hypotheses researchers have put forth to explain how outcomes of socially mobile and immobile individuals might differ and/or how mobility experiences are related to outcomes of interest. Next, we examine the methodological literature on this topic, culminating in the development of the diagonal mobility model (DMM, also called the diagonal reference model in some studies), the primary tool of use since the 1980's. We then discuss some of the many applications of the DMM. Although the model was proposed to examine the effects of social mobility on outcomes of interest, the estimated relationships between mobility and outcomes that researchers have called mobility effects are more appropriately regarded as partial associations. When mobility is not associated with outcomes, as is often found in empirical work, the outcomes of movers from origin o to destination d are a weighted average of the outcomes of individuals who remained in states o and d respectively, and the weights capture the relative salience of origins and destinations in the acculturation process. In light of this attractive feature of the model, we briefly develop several generalizations of the current DMM that future researchers should also find useful. Finally, we propose new estimands of mobility effects, based on the explicit notion that a unit effect of mobility is a comparison of an individual with herself under two conditions, one in which she is mobile, the other in which she is immobile, and we discuss some of the challenges in identifying such effects.

Job loss and fetal growth restriction: identification of critical trimesters of exposure

PURPOSE

Previous research suggests that job loss in a household during pregnancy may perturb fetal growth. However, this work often cannot rule out unmeasured confounding due to selection into job loss. Recent work using data on exogenous job loss (due to a plant closure) finds that a father's unexpected job loss during his spouse's pregnancy increases the risk of a low weight birth. Using a unique set of linked registries in Denmark, we build on this work and examine whether associations between a father's unexpected job loss and low birthweight differ by trimester of in utero exposure. We additionally examine trimester-specific associations of job loss with small-for-gestational-age, a proxy for restricted fetal growth, which may cause low birthweight.

METHODS

We apply a sibling control design to over 1.4 million live births in Denmark, 1980 to 2017, to examine whether this plausibly exogenous form of job loss corresponds with increased risk of low weight or small-for-gestational-age births, depending on the timing of displacement in the first, second, or third trimester.

RESULTS

Results indicate an elevated risk of low birthweight (OR = 1.80, 95% CI: 1.24, 2.62) and small-for-gestational-age (OR = 1.40, 95% CI: 1.02, 1.93) among gestations exposed to job loss in the second trimester of pregnancy. Sensitivity analyses using continuous outcome measures (e.g., birthweight in grams, birthweight for gestational age percentile) and maternal fixed effects analyses produce substantively similar inference.

CONCLUSIONS

Findings support the notion that unexpected job loss may affect fetal growth and that the second trimester in particular appears sensitive to this external stressor.

The Role of Conditional Likelihoods in Latent Variable Modeling

In psychometrics, the canonical use of conditional likelihoods is for the Rasch model in measurement. Whilst not disputing the utility of conditional likelihoods in measurement, we examine a broader class of problems in psychometrics that can be addressed via conditional likelihoods. Specifically, we consider cluster-level endogeneity where the standard assumption that observed explanatory variables are independent from latent variables is violated. Here, "cluster" refers to the entity characterized by latent variables or random effects, such as individuals in measurement models or schools in multilevel models and "unit" refers to the elementary entity such as an item in measurement. Cluster-level endogeneity problems can arise in a number of settings, including unobserved confounding of causal effects, measurement error, retrospective sampling, informative cluster sizes, missing data, and heteroskedasticity. Severely inconsistent estimation can result if these challenges are ignored.

Causal Inference with Genetic Data: Past, Present, and Future

The set of methods discussed in this collection has emerged from the convergence of two scientific fields-genetics and causal inference. In this introduction, we discuss relevant aspects of each field and show how their convergence arises from the natural experiments that genetics offer. We present introductory concepts useful to readers unfamiliar with genetically informed methods for causal inference. We conclude that existing applications and foreseeable developments should ensure that we rapidly reap the rewards of this relatively new field, not only in terms of our understanding of human disease and development, but also in terms of tangible translational applications.

Pre-eclampsia and risk of early-childhood asthma: a register study with sibling comparison and an exploration of intermediate variables

BACKGROUND

We aimed to study whether pre-eclampsia is associated with childhood asthma, allergic and non-allergic asthma, accounting for family factors and intermediate variables.

METHODS

The study population comprised 779 711 children born in 2005-2012, identified from Swedish national health registers (n = 14 823/7410 exposed to mild/moderate and severe pre-eclampsia, respectively). We used Cox regression to estimate the associations of mild/moderate and severe pre-eclampsia with incident asthma, before and after age 2 years. Cox regressions were controlled for familial factors using sibling comparisons, then stratified on high and low risk for intermediate variables: caesarean section, prematurity and small for gestational age. We used logistic regression for allergic and non-allergic prevalent asthma at 6 years as a measure of more established asthma.

RESULTS

The incidence of asthma in children was 7.7% (n = 60 239). The associations varied from adjusted hazard ratio (adjHR) 1.11, 95% confidence interval (CI): 1.00, 1.24 for mild/moderate pre-eclampsia and asthma at >2 years age, to adjHR 1.78, 95% CI: 1.64, 1.95 for severe pre-eclampsia and asthma at <2 years age. Sibling comparisons attenuated most estimates except for the association between severe pre-eclampsia and asthma at <2 years age (adjHR 1.45, 95% CI: 1.10, 1.90), which also remained when stratifying for the risk of intermediates. Mild/moderate and severe pre-eclampsia were associated with prevalent non-allergic (but not allergic) asthma at 6 years, with adjusted odds ratio (adjOR) 1.17, 95% CI: 1.00, 1.36 and adjOR 1.51, 95% CI: 1.23, 1.84, respectively.

CONCLUSIONS

We found evidence that severe, but not mild/moderate, pre-eclampsia is associated with asthma regardless of familial factors and confounders.

Maternal vitamin D intake and BMI during pregnancy in relation to child's growth and weight status from birth to 8 years: a large national cohort study

OBJECTIVES

To examine the associations between maternal vitamin D intake and childhood growth and risk of overweight up to 8 years. We further examined the effect modification by maternal prepregnancy body mass index (BMI).

DESIGN

Prospective population-based pregnancy cohort study.

SETTING

The Norwegian Mother, Father and Child Cohort Study.

PARTICIPANTS

In total, 58 724 mothers and 66 840 singleton children, with information on maternal vitamin D intake during the pregnancy and minimum one postnatal anthropometric measurement.

OUTCOME MEASURES

Predicted weight and height growth trajectories and velocities from 1 month to 8 years, rapid growth during infancy and toddlerhood, and risk of overweight in preschool and school age.

RESULTS

Overall, maternal vitamin D intake was associated with lower weight trajectory, lower odds of rapid weight growth and higher odds of childhood overweight. In children of mothers with prepregnancy normal weight, maternal vitamin D intake was negatively associated with weight trajectory and lower OR of a rapid weight growth during the first year, compared with reference (<5 µg/day). Children of mothers with normal weight, with maternal vitamin D intakes of 10-15 and >15 µg/day, also had 0.86 (95% CI 0.77 to 0.97) and 0.88 (95% CI 0.79 to 0.99) lower odds for overweight at 3 years, compared with reference. In contrast, in children of mothers with prepregnancy overweight (BMI ≥25 kg/m²), vitamin D intake was positively associated with weight trajectory. Children of mothers with overweight, with maternal vitamin D intake of 5-9.9 µg/day, also had (1.09 (95% CI 1.01 to 1.18) and 1.12 (95% CI 1.02 to 1.23)) higher odds for overweight at 5 years and 8 years, compared with reference.

CONCLUSIONS

Maternal vitamin D intake affects postnatal growth and is inversely associated with childhood overweight in children of mothers with normal weight. Associations between maternal vitamin D intake and child growth and risk of overweight varied by prepregnancy BMI.

Maternal seafood intake during pregnancy, prenatal mercury exposure and child body mass index trajectories up to 8 years

BACKGROUND

Maternal seafood intake during pregnancy and prenatal mercury exposure may influence children's growth trajectories.

METHODS

This study, based on the Norwegian Mother, Father and Child Cohort Study (MoBa), includes 51 952 mother-child pairs recruited in pregnancy during 2002-08 and a subsample (n = 2277) with maternal mercury concentrations in whole blood. Individual growth trajectories were computed by modelling based on child's reported weight and length/height from 1 month to 8 years. We used linear mixed-effects regression analysis and also conducted discordant-sibling analysis.

RESULTS

Maternal lean fish was the main contributor to total seafood intake in pregnancy and was positively but weakly associated with child body mass index (BMI) growth trajectory. Higher prenatal mercury exposure (top decile) was associated with a reduction in child's weight growth trajectory, with the estimates ranging from -130 g [95% Confidence Intervals (CI) = -247, -12 g] at 18 months to -608 g (95% CI = -1.102, -113 g) at 8 years. Maternal fatty fish consumption was positively associated with child weight and BMI growth trajectory, but only in the higher mercury-exposed children (P-interaction = 0.045). Other seafood consumption during pregnancy was negatively associated with child weight growth compared with no intake, and this association was stronger for higher mercury-exposed children (P-interaction = 0.004). No association was observed between discordant maternal seafood intake and child growth in the sibling analysis.

CONCLUSIONS

Within a population with moderate seafood consumption and low mercury exposure, we found that maternal seafood consumption in pregnancy was associated with child growth trajectories, and the direction of the association varied by seafood type and level of prenatal mercury exposure. Prenatal mercury exposure was negatively associated with child growth. Our findings on maternal seafood intake are likely non-causal.

Systematic Review and Meta-analysis of Genetically Informed Research: Associations Between Parent Anxiety and Offspring Internalizing Problems

OBJECTIVE

Parent anxiety is associated with offspring internalizing problems (emotional problems related to anxiety and depression). This may reflect causal processes, whereby exposure to parent anxiety directly influences offspring internalizing (and/or vice versa). However, parent-offspring associations could also be attributable to their genetic relatedness. A systematic review and meta-analysis were conducted to investigate whether exposure to parent anxiety is associated with offspring internalizing after controlling for genetic relatedness.

METHOD

A literature search across 5 databases identified 429 unique records. Publications were retained if they used a quasi-experimental design in a general population sample to control for participant relatedness in associations between parent anxiety and offspring internalizing outcomes. Publications were excluded if they involved an experimental exposure or intervention. Studies of prenatal and postnatal anxiety exposure were meta-analyzed separately. Pearson's correlation coefficient estimates (r) were pooled using multilevel random-effects models.

RESULTS

Eight publications were retained. Data were drawn from 4 population cohorts, each unique to a quasi-experimental design: adoption, sibling-comparison, children-of-twins or in vitro fertilization. Cohorts were located in northern Europe or America. Families were predominantly of European ancestry. Three publications (Nfamilies >11,700; offspring age range, 0.5-10 years) showed no association between prenatal anxiety exposure and offspring internalizing outcomes after accounting for participant relatedness (r = .04; 95% CI: -.07, .14). Six publications (Nfamilies >12,700; offspring age range, 0.75-22 years) showed a small but significant association between concurrent symptoms in parents and offspring after accounting for participant relatedness (r = .13; 95% CI: .04, .21).

CONCLUSION

Initial literature, derived from homogeneous populations, suggests that prenatal anxiety exposure does not cause offspring internalizing outcomes. However, postnatal anxiety exposure may be causally associated with concurrent offspring internalizing via nongenetic pathways. Longitudinal stability, child-to-parent effects, and the role of moderators and methodological biases require attention.

Invited Commentary: Sibling-Comparison Designs, Are They Worth the Effort?

In this issue of the Journal, von Ehrenstein et al. (Am J Epidemiol. 2021;190(5):728-737) add to the large and growing literature on the potentially causal association between prenatal exposure to maternal smoking and neuropsychiatric health. In addition to statewide, prospectively collected data, a particular strength was their ability to perform a sibling-comparison design, contrasting the rate of autism spectrum disorder in siblings discordantly exposed to maternal smoking. Unfortunately, the estimate from the sibling pairs could neither confirm nor refute the conclusions based on the full cohort. Interpretation was hampered by broad confidence limits, and even had power been higher, the authors acknowledge a range of potential biases that would have made it difficult to draw any firm conclusions from a similarity or difference in the sibling-pair estimate and estimate from the full cohort. Was the addition of the sibling comparison actually worth the effort? In this commentary, I will briefly summarize the benefits and limitations of this design, and, with some caveats, argue that its inclusion in the study by von Ehrenstein et al. was indeed a strength and not just an ornamentation.

Under-5 mortality and morbidity outcomes of fertility postponement in Turkey: explanations by observed and unobserved characteristics

This paper investigates the association between advanced maternal age and under-5 mortality and morbidity in Turkey, and is the first such study in the country to use a sibling comparison model to analyze this phenomenon. The study is based on data obtained from the 2013 Turkey Demographic and Health Survey, and analyzes the association of advanced maternal age with: (1) under-five mortality, using Cox proportional hazard models and their stratified versions to compare sibling groups born to the same mother in the 1978-2013 period, and (2) under-five morbidity; specifically, being born with low birth weight, stunting, underweight, and wasting based on between- and within-sibling groups models for the 2008-2013 period. Overall, our findings suggest that the hazard of under-5 mortality increases as maternal age increases. We conclude that period effects have failed to reverse the impeding effects of advanced maternal age on child mortality. Between-sibling group models indicate a positive but close to null association between advanced maternal age and child morbidity in general, although these positive associations vanish once we apply within-sibling group models. This result can be partially attributed to our controlling for unobserved characteristics specific to sibling groups, in addition to other methodological differences.

Parental age and birth defects: a sibling study

Higher parental age at childbearing has generated much attention as a potential risk factor for birth disorders; however, previous research findings are mixed. Existing studies have exploited variation in parental age across families, which is problematic because families differ not only in parental age but also in genetic and environmental factors. To isolate the effects of parental age, holding many genetic and environmental factors constant, we exploit the variation in parental age within families and compare outcomes for full siblings. The study data were retrieved from the Medical Birth Registry of Norway, which covers the entire population of births in Norway over an extended period (totaling 1.2 million births). Using variation in parental age when siblings were born, we find large and convex effects of increased parental age on the increased risk of birth disorders. To facilitate comparison with the existing literature, we also estimate the effects of parental age using variation in parental age across families and find that the effects are substantially weaker. We conclude that the existing literature may have underestimated the negative effects of parental aging on adverse offspring outcomes.

Family-Based Designs that Disentangle Inherited Factors from Pre- and Postnatal Environmental Exposures: In Vitro Fertilization, Discordant Sibling Pairs, Maternal versus Paternal Comparisons, and Adoption Designs

Identifying environmental risk and protective exposures that have causal effects on health is an important scientific goal. Many environmental exposures are nonrandomly allocated and influenced by dispositional factors including inherited ones. We review family-based designs that can separate the influence of environmental exposures from inherited influences shared between parent and offspring. We focus on prenatal exposures. We highlight that the family-based designs that can separate the prenatal environment from inherited confounds are different to those that are able to pull apart later-life environmental exposures from inherited confounds. We provide a brief review of the literature on maternal smoking during pregnancy and offspring attention-deficit/hyperactivity disorder (ADHD) and conduct problems; these inconsistencies in the literature make a review useful and this illustrates that results of family-based genetically informed studies are inconsistent with a causal interpretation for this exposure and these two offspring outcomes.

Twin Differences in Harsh Parenting Predict Youth's Antisocial Behavior

In the current study, we leveraged differences within twin pairs to examine whether harsh parenting is associated with children's antisocial behavior via environmental (vs. genetic) transmission. We examined two independent samples from the Michigan State University Twin Registry. Our primary sample contained 1,030 families (2,060 twin children; 49% female; 6-10 years old) oversampled for exposure to disadvantage. Our replication sample included 240 families (480 twin children; 50% female; 6-15 years old). Co-twin control analyses were conducted using a specification-curve framework, an exhaustive modeling approach in which all reasonable analytic specifications of the data are interrogated. Results revealed that, regardless of zygosity, the twin experiencing harsher parenting exhibited more antisocial behavior. These effects were robust across multiple operationalizations and informant reports of both harsh parenting and antisocial behavior with only a few exceptions. Results indicate that the association between harsh parenting and children's antisocial behavior is, to a large degree, environmental in origin.

Nurture might be nature: cautionary tales and proposed solutions

Across a wide range of studies, researchers often conclude that the home environment and children's outcomes are causally linked. In contrast, behavioral genetic studies show that parents influence their children by providing them with both environment and genes, meaning the environment that parents provide should not be considered in the absence of genetic influences, because that can lead to erroneous conclusions on causation. This article seeks to provide behavioral scientists with a synopsis of numerous methods to estimate the direct effect of the environment, controlling for the potential of genetic confounding. Ideally, using genetically sensitive designs can fully disentangle this genetic confound, but these require specialized samples. In the near future, researchers will likely have access to measured DNA variants (summarized in a polygenic scores), which could serve as a partial genetic control, but that is currently not an option that is ideal or widely available. We also propose a work around for when genetically sensitive data are not readily available: the Familial Control Method. In this method, one measures the same trait in the parents as the child, and the parents' trait is then used as a covariate (e.g., a genetic proxy). When these options are all not possible, we plead with our colleagues to clearly mention genetic confound as a limitation, and to be cautious with any environmental causal statements which could lead to unnecessary parent blaming.