The similarity of siblings' attachments to their mother

Do siblings develop similar attachment relationships with their mother? Att achment theory suggests that brothers and sisters growing up in the same fa mily are likely to relate in similar ways to their parents, at least when p arental attachment representations and interactive styles remain stable acr oss time. In the current study, sibling attachment data from three research groups (from Pennsylvania State University, Leiden University, and the Uni versity of Western Ontario) have been pooled to assemble a sufficiently lar ge sample of observations (N = 138 sibling pairs) for a detailed comparison of sibling attachment relationships. Spacing between the births, differenc es in maternal sensitivity, and gender of siblings were examined as possibl e sources of concordance of nonconcordance. Attachment security (including disorganized attachment) of each sibling was assessed with the Strange Situ ation procedure between 12 and 14 months after birth. Maternal sensitivity was observed with the same rating scale in a laboratory play session in one of the studies and in home observations in the others. Sibling relationshi ps were found to be significantly concordant when classified as secure/nons ecure (62% concordance, p < .01, 1-tailed, intraclass correlation = .23) bu t not when further subcategorized. Maternal insensitivity to both siblings (shared environment) was associated with concordance of sibling nonsecurity . Siblings of the same gender were more likely to form concordant relations hips with their mother (68%; p < .01, 1-tailed, intraclass correlation = .3 7) than those of opposite gender. Same-sex sibling concordance was comparab le to the concordance found for monozygotic twins in earlier studies. Genet ic factors may, therefore, play a relatively small role in the development of attachment.