Children with additional siblings appear to fare worse on a variety of developmental and educational outcomes across social contexts. Yet, the causal relation between sibship size and later attainment remains dubious, as factors that influence parents’ fertility decisions also shape children’s socioeconomic prospects. We apply instrumental variables methods that treat multiple births (e.g., twins, triplets) and same-sex composition as natural experiments to test whether increases in sibship size have a causal effect on the educational attainment of older siblings in the U.S. We pool several nationally representative datasets, including the Child and Young Adult Cohorts of the NLSY79 and the Panel Study of Income Dynamics, to obtain adequate sample sizes for these methods. Although results indicate that the presence of an additional sibling has a trivial effect on the attainment of older siblings for most families (those with two to four siblings), a large penalty arises with the introduction of a fifth sibling. Our findings imply that the costs associated with sibship size are likely concentrated among the largest families.

在社会背景下，具有其他兄弟姐妹的孩子在各种发展和教育成果上的表现似乎更差。然而，由于影响父母的生育力决定的因素也影响着孩子的社会经济前景，同胞人数和以后的成就之间的因果关系仍然令人怀疑。我们采用工具变量方法，将多胎（例如双胞胎，三胞胎）和同性组成作为自然实验进行处理，以检验同胞数量的增加是否对美国年长同胞的教育程度产生因果关系。数据集，包括NLSY79的儿童和年轻成人队列以及收入动态小组研究，以获得这些方法的足够样本量。尽管结果表明，对于大多数家庭（那些有两到四个兄弟姐妹），增加兄弟姐妹对获得年长兄弟姐妹的影响微不足道，但是引入第五个兄弟姐妹会产生较大的惩罚。我们的研究结果表明，与同胞生活相关的成本可能集中在最大的家庭中。