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.

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.

Alcohol Exposure In Utero and Child Academic Achievement.

We examine the effect of alcohol exposure in utero on child academic achievement. As well as studying the effect of any alcohol exposure, we investigate the effect of the dose, pattern, and duration of exposure. We use a genetic variant in the maternal alcohol-metabolism gene ADH1B as an instrument for alcohol exposure, whilst controlling for the child's genotype on the same variant. We show that the instrument is unrelated to an extensive range of maternal and paternal characteristics and behaviours. OLS regressions suggest an ambiguous association between alcohol exposure in utero and children's academic attainment, but there is a strong social gradient in maternal drinking, with mothers in higher socio-economic groups more likely to drink. In stark contrast to the OLS, the IV estimates show negative effects of prenatal alcohol exposure on child educational attainment. These results are very robust to an extensive set of model specifications. In addition, we show that that the effects are solely driven by the maternal genotype, with no impact of the child's genotype.

School meal crowd out in the 1980s.

This paper explores whether the state provision of school meals in the 1980s crowded out private provision by examining two policy reforms that radically altered the UK school meal service. Both reforms effectively increased the cost of school meals for one group (the treated), leaving another unaffected (the controls). I find strong evidence of crowd out: the reforms reduced school meal take-up among the treated by 20-30 percentage points, with no difference among the controls. I then examine whether this affected children's body weights, using a large, unique, longitudinal dataset of primary school children from 1972 to 1994. The findings show no evidence of any effects on child body weight.

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 children's 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 effect of fat mass on educational attainment: examining the sensitivity to different identification strategies.

The literature that examines the relationship between child or adolescent Body Mass Index (BMI) and academic attainment generally finds mixed results. This may be due to the use of different data sets, conditioning variables, or methodologies: studies either use an individual fixed effects (FE) approach and/or an instrumental variable (IV) specification. Using one common dataset, the Avon Longitudinal Study of Parents and Children, and a common set of controls, this paper compares the different approaches (including using different types of IV's), discusses their appropriateness, and contrasts their findings. We show that, although the results differ depending on the approach, most estimates cannot be statistically distinguished from OLS, nor from each other. Examining the potential violations of key assumptions of the different approaches and comparing their point estimates, we conclude that fat mass is unlikely to be causally related to academic achievement in adolescence.

Maternal employment and overweight children: does timing matter?

Recent literature has shown consistent evidence of a positive relationship between maternal employment and children's overweight status. These studies largely use average weekly work hours over the child's 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.