Duke 2008 | ASHE | Equity and Efficiency in Health and Healthcare

Economists and other social scientists have recently examined the relationship between birth order and risky adolescent behaviors. The results suggest that, controlling for family size and other background characteristics, children with older siblings are more likely to have used tobacco, alcohol and marijuana, and are more likely to have had sexual intercourse than firstborn children. There are a number of possible explanations for why having an older sibling might lead to negative behaviors such as substance use and sexual activity. For instance, it may be that older adolescents influence their younger siblings either purposely or inadvertently. Alternatively, parents may adopt different rules or attitudes toward monitoring and supervising their subsequent offspring as compared to their firstborns

In this paper we use data from the National Longitudinal Survey of Adolescent Health (AddHealth) to extend the analysis to consider the relationship between birth order and health behaviors and outcomes. Creating detailed information on the age, sex and residential location of the sibling of the respondents, we begin our analysis with an examination of the effect of having an older sibling (and more detailed measures of birth order) on the incidence of overweight and obesity among adolescents. Our models will control for family characteristics that might be correlated with birth order such as family size, family structure and socioeconomic characteristics of the family. Our preliminary analyses suggest that there is a clear association between the presence of an older sibling and the probability of being overweight or obese. We then extend these models to identify the possible contributions of differences in parental supervision or permissiveness vs. the more direct route through sibling effects. If later born children are less likely to be supervised by their parents, and are less likely to have a parent present after school or in the evenings, children’s nutrition and exercise patterns may be less healthy than for their firstborn counterparts. The AddHealth data contain information regarding the regular presence of parents before school, after school and at bedtime. We will include these variables to see of the effect of birth order on BMI is caused primarily by differences in supervision by birth order.

The other possible explanation for the observed correlation between having an older sibling and being overweight or obese is that the older sibling exerts a direct influence on their younger sibling. It is possible that the older sibling is more body or image conscious due to societal norms that older siblings are potentially more likely to be exposed to. Though we do not have a direct measure of this, we do know if the younger sibling is dieting and we have information on their body image. Using this information, we model the association between the presence of an older sibling, and sibling characteristics such as age, sex and residential arrangement, on an adolescent’s body image and dieting behavior. Controlling for the adolescent’s BMI in these models will enable us to identify the contribution of siblings to misperceptions of body image.