Stephanie von Hinke Kessler Scholder

Maternal employment and overweight children: does timing matter?

Recent literature has shown consistent evidence of a positive relationship between maternal employment and childrens overweight status. These studies largely use average weekly work hours over the childs life to measure employment. This paper specifically aims at exploring the importance of the timing of employment. Using various econometric techniques to control for observable and unobservable child and family characteristics, the results show that full-time maternal employment during mid-childhood positively affects the probability of being overweight at age 16. There is no evidence that part-time or full-time employment at earlier/later ages affects this probability.

The effect of fat mass on educational attainment: Examining the sensitivity to different identification strategies

Highlights ► We examine the effect of adolescent adiposity on educational outcomes. ► We compare the findings using different approaches used in the literature. ► We use an individual fixed effects as well as IV approach, with different sets of instruments. ► We conclude that adiposity is unlikely to causally affect academic achievement in adolescence.

*Smarter Task Assignment or Greater Effort: The Impact of Incentives on Team Performance

We use an experiment to study the impact of team-based incentives, exploiting rich data from personnel records and management information systems. Using a triple difference design, we show that the incentive scheme had an impact on team performance, even with quite large teams. We examine whether this effect was due to increased effort from workers or strategic task reallocation. We find that the provision of financial incentives did raise individual performance but that managers also disproportionately reallocated efficient workers to the incentivised tasks. We show that this reallocation was the more important contributor to the overall outcome.

The many weak instruments problem and Mendelian randomization

Instrumental variable estimates of causal effects can be biased when using many instruments that are only weakly associated with the exposure. We describe several techniques to reduce this bias and estimate corrected standard errors. We present our findings using a simulation study and an empirical application. For the latter, we estimate the effect of height on lung function, using genetic variants as instruments for height. Our simulation study demonstrates that, using many weak individual variants, two-stage least squares (2SLS) is biased, whereas the limited information maximum likelihood (LIML) and the continuously updating estimator (CUE) are unbiased and have accurate rejection frequencies when standard errors are corrected for the presence of many weak instruments. Our illustrative empirical example uses data on 3631 children from England. We used 180 genetic variants as instruments and compared conventional ordinary least squares estimates with results for the 2SLS, LIML, and CUE instrumental variable estimators using the individual height variants. We further compare these with instrumental variable estimates using an unweighted or weighted allele score as single instruments. In conclusion, the allele scores and CUE gave consistent estimates of the causal effect. In our empirical example, estimates using the allele score were more efficient. CUE with corrected standard errors, however, provides a useful additional statistical tool in applications with many weak instruments. The CUE may be preferred over an allele score if the population weights for the allele score are unknown or when the causal effects of multiple risk factors are estimated jointly.

Child height, health and human capital: evidence using genetic markers

Height has long been recognized as being associated with better outcomes: the question is whether this association is causal. We use childrens genetic variants as instrumental variables to deal with possible unobserved confounders and examine the effect of child/adolescent height on a wide range of outcomes: academic performance, IQ, self-esteem, depression symptoms and behavioral problems. OLS findings show that taller children have higher IQ, perform better in school, and are less likely to have behavioral problems. The IV results differ: taller girls (but not boys) have better cognitive performance and, in contrast to the OLS, greater height appears to increase behavioral problems.

The Demand for Cigarettes as Derived from the Demand for Weight Loss: A Theoretical and Empirical Investigation

This paper offers an economic model of smoking and body weight and provides new empirical evidence on the extent to which the demand for cigarettes is derived from the demand for weight loss. In the model, smoking causes weight loss in addition to having direct utility benefits and direct health consequences. It predicts that some individuals smoke for weight loss and that the practice is more common among those who consider themselves overweight and those who experience greater disutility from excess weight. We test these hypotheses using nationally representative data in which adolescents are directly asked whether they smoke to control their weight. We find that, among teenagers who smoke frequently, 46% of girls and 30% of boys are smoking in part to control their weight. As predicted by the model, this practice is significantly more common among those who describe themselves as too fat and among groups that tend to experience greater disutility from obesity. We conclude by discussing the implications of these findings for tax policy; specifically, the demand for cigarettes is less price elastic among those who smoke for weight loss, all else being equal. Public health efforts to reduce smoking initiation and encourage cessation may wish to design campaigns to alter the derived nature of cigarette demand, especially among adolescent girls.

Alcohol Exposure In Utero and Child Academic Achievement

We examine the effect of prenatal alcohol exposure on child academic achievement. We use a genetic variant in the maternal alcohol-metabolism gene ADH1B to instrument for alcohol exposure, whilst controlling for the childs genotype on the same variant. We show that the instrument is unrelated to an extensive range of parental characteristics and behaviour. OLS regressions suggest an ambiguous association between alcohol exposure and attainment but there is a strong social gradient in drinking, with mothers in higher socio-economic groups more likely to drink. In contrast to the OLS, the IV estimates show clear negative effects of prenatal alcohol exposure.

Genetic Instrumental Variable Studies of Effects of Prenatal Risk Factors

Identifying the effects of maternal risk factors during pregnancy on infant and child health is an area of tremendous research interest. However, policymakers are primarily interested in unraveling the causal effects of prenatal risk factors, not their associations with child health, which may be confounded by several unobserved factors. In this article, we evaluate the utility of genetic variants in three genes that have unequivocal evidence of being related to three major risk factors—CHRNA3 for smoking, ADH1B for alcohol use, and FTO for obesity—as instrumental variables for identifying the causal effects of such factors during pregnancy. Using two independent datasets, we find that these variants are overall predictive of the risk factors and are not systematically related to observed confounders, suggesting that they may be useful instruments. We also find some suggestive evidence that genetic effects are stronger during than before pregnancy. We provide an empirical example illustrating the use of these genetic variants as instruments to evaluate the effects of risk factors on birth weight. Finally, we offer suggestions for researchers contemplating the use of these variants as instruments. Data analysis of the DNBC dataset was supported by NIH/NIDCR grant 1 R01 DE020895. We are extremely grateful to all the families who took part in the DNBC and ALSPAC studies; the staff and midwives for their help in recruiting them; and the whole ALSPAC team, which includes interviewers, computer and laboratory technicians, clerical workers, research scientists, volunteers, managers, receptionists, and nurses. The UK Medical Research Council, the Wellcome Trust, and the University of Bristol provide core support for ALSPAC. This publication is the work of the authors and does not reflect the views of the ALSPAC executive. We thank Drs. Mads Melbye and Jeffrey C. Murray for providing access to the DNBC data. We also thank Dr. Bjarke Feenstra for his thoughtful review of the paper.