Effects of Sibling Number on Child Outcome

This article reviews studies concerning the impact of sibling number on a selected series of outcomes including IQ, educational attainment, status of current job, and current earnings, Sibling number is a variable over time and cannot be properly measured unless data are available on the number and timing of all births and the age at which each child in the family ceases to be dependent. Unfortunately, existing research is too much based on secondary analysis of data sets for which all of the requisite information is not available. Controversies surround the question whether there is a causal impact of sibling number on IQ and, if so, how it can be explained; these are reviewed in detail. Research on the impact of sibling number on the other three dependent variables is reviewed, particularly where it contributes to our knowledge of the impact on educational attainment net of IQ, on job status net of education attainment, and on current earnings net of job status. It is concluded that decisions on the number and spacing of children are among the most important decisions parents can make. Therefore the large amounts of funds needed for data collection will be funds well spent.