Statistical sensitivity analysis for the estimation of fetal alcohol spectrum disorders prevalence.

Fetal alcohol spectrum disorders (FASD) are thought to be the leading cause of developmental disabilities worldwide. Accurate estimates of the prevalence of FASD have been lacking. An improved estimate of FASD prevalence in the U.S. was recently reported in a study where multistage methods of active case ascertainment of first-grade children with FASD were utilized in four regions in the U.S. Each method relied on parental consent and therefore had potential non-response bias. We consider weighted approaches, where the weights were formed using the distribution of observed variables in the population from which the samples were drawn. However, there are likely other unobserved variables that affect both non-response and FASD outcome. We describe sensitivity analyses using methodology developed for causal inference. The results show feasible regions of FASD prevalence under certain assumptions, and provide a framework for explaining the non-response bias due to the unobserved variables.