Using Sibling Designs to Understand Development

Abstract

Although sibling relationships, and particularly sibling rivalry, have featured prominently in religious texts, literature, and the popular media (Bart Simpson would certainly not be the same without his foil of a sister Lisa), siblings are often neglected in scientific research. Even among family researchers, the prominence of the parentchild relationship in comparison to the sibling relationship is staggering. A perusal of this year's Society for Research in Child Development program yields a ratio of 20:1 for parent-child: sibling presentations. This is in spite of the fact that children's time spent with siblings often outstrips that spent with parents (Larson & Richards, 1994), and that in some cases the contribution of siblings is at least as great as that made by parents in fields as diverse as gender development (McHale, Updegraff, Helms-Erikson, & Crouter, 2001) and antisocial behaviour (Garcia, Shaw, Winslow, & Yaggi, 2000).As well as the sibling relationship being an important context for children's individual development-as some of the articles in the issue will demonstrate-data from siblings also allow for specialized analytic possibilities. When I was invited to guest edit a special issue about siblings, it was the opportunity to disseminate these methodological prospects that appealed to me. Therefore, I solicited contributions that would demonstrate the value of sibling designs, regardless of whether a researcher is interested in siblings per se.The crux of sibling designs is that they allow researchers to examine within-family processes as well as between-family processes. Arguably, we have behavioral geneticists to thank for our appreciation of within-family effects. In 1987, Robert Plomin and Denise Daniels published an article, "Why are children in the same family so different from each other?" which highlighted the fact that once genes are taken into account, most environmental influence works within families, making siblings different to one another, rather than between families (which would lead to sibling similarity). The articles that make up this special issue showcase different techniques that have been developed to understand children's development using sibling designs to pinpoint both between-and within-family processes.The first article by Richmond and Stocker (2009) uses a difference score approach to quantify within-family variation. Sibling differences in experience of marital conflict and parent-child hostility are shown to link with sibling differences in the children's externalizing problems. This elegant tool has stood the test of time because it is a simple, elegant, powerful method that is unsurpassed in terms of reader friendliness.In the second article Tina Kretschmer and I (Pike & Kretschmer, 2009) use structural equation modelling to quantify both shared (between-family) and nonshared (within-family) sources of correlation. This method is a simplification of models developed for twin and/or adoption data by behavioral geneticists. In our exemplar