The Population Level Impacts of Differential Fertility Behavior of Parents of Children with Autism

Abstract

Abstract:Drawing on population level data of exceptional quality (including detailed diagnostic information on the autism status of sibling pairs of over 3 million different mothers), this study confirms that stoppage is the average fertility response to a child born with autism, thereby reducing observed concordance in sibling pairs and leading to potentially biased estimation of genetic contributions to autism etiology. Using a counterfactual framework and applying matching techniques we show, however, that this average effect is composed of very different responses to suspicion of autism depending on birth cohort, the character of the disorder (severe versus less severe), the gender of the child, poverty status, and parental education. This study also sheds light on when parents suspect autism. We find that parents' fertility behavior changes relative to matched controls very early after the birth of a child who will later be diagnosed with autism.Keywords: autism; fertility; matching; causal inference; effect heterogeneity W E examine the fertility behavior of mothers of children with autism, using a methodological approach that allows us to estimate the effect of suspicion of a first child's autism status on subsequent fertility. In doing so, we provide an improved foundation for autism recurrence rate estimation and reveal patterns of differential ascertainment, illustrating the importance of considering heterogeneity in the autism status of firstborn children as a "treatment," as well as heterogeneity in its effects. Our results reveal when "stoppage"-a decision not to have subsequent children due to the autism status of one's first child-occurs, and demonstrate the importance of integrating demographic decisions into models of heritability.Prior literature has examined the fertility decisions of parents of children with autism because of their implications for the estimation of an accurate recurrence rate. Autism is widely believed to be one of the most "genetic" of developmental disorders (Abrahams and Geschwind 2008;Lamb, Bailey, and Monaco 2000;Wang et al. 2009). In the absence of known genetic markers, a classic way to ascertain whether a disorder is genetic is to conduct a family resemblance study where concordance of the disorder in twins is compared to concordance in full and half siblings. Only a few such studies have been conducted with respect to autism, yielding strikingly high estimates for recurrence risk. Using population level data, Liu, Zerubavel, and Bearman (2010a) found concordance rates of 47.5 percent in same-sex twins, 9.7 percent in full siblings, and 3.4 percent in half siblings. The fact that autism is at least partly genetically determined has real consequences. High heritability estimates shape the allocation of research priorities as well as lay understanding, potentially contributing to family-planning decisions. Family resemblance studies by definition require restricting the population under study to families with more than one child. If parents react to the birth of a chil...