Persistence in body mass index in a recent cohort of US children

- Anthropometric data on U.S. primary school children are analyzed.
- Nonparametric metrics are proposed to assess anthropometric dynamics.
- Dynamics follow a U-shaped pattern, with greater movements among the young and old.
- Patterns in persistence differ in important ways across demographic groups.

While childhood obesity has become a significant public health concern over the last few decades, and underweight children continue to be a concern, knowledge pertaining to the origins of or persistence in childhood anthropometric measures is incomplete. Here, we utilize several nonparametric metrics to assess the evolution of weight and body mass index (BMI) across the entire distribution during early childhood. We find that movements within the distribution of weight - both upward and downward - are quite high prior to primary school and then decline noticeably. For BMI, we find that movements within the distribution - both upward and downward - are highest at the start of kindergarten and at the start of middle school. However, there are important sources of heterogeneity, including race, gender, and age that should prove insightful to researchers and policymakers. For instance, comparing males versus females who are initially in the bottom quartile of the distribution of BMI, we find that males have a higher probability of moving up at least 10 percentile points between kindergarten and eighth grade (53% versus 50%). Comparisons among racial groups indicate that whites who are initially in the top quartile of the distribution of BMI have a higher probability of moving down at least 10 percentile points between kindergarten and eighth grade than blacks and Hispanics (46% versus 37% and 40%, respectively).