The Reliability and Stability of Individual Differences in Infant-Mother Attachment

50 infants were seen twice in the Ainsworth and Wittig Strange Situation to assess individual differences in the quality of infant-mother attachment at 12 and at 18 months of age. Evidence for the stability of individual differences was clearly a function of the level of analysis. The reliability of discrete-behavior variables was typically very low, and there was little evidence of temporal stability. There was clear evidence for stable individual differences in the analysis of behavior category data. This was especially true of behavior toward the mother during reunion after brief separations. Classification data based largely on reunion behavior and crying were even more stable across the 6-month interval. Each infant was assigned to 1 of 3 categories (secure/normative, avoidant, or ambivalent) on the basis of the patterning of attachment behavior at 12 months. 48 of the 50 infants were independently reassigned to the same category on the basis of the same behaviors at 18 months. In contrast to time sampling of phenotypically similar discrete behaviors, assessments which take into account the behavioral context of behavior yield more reliable assessments of individual differences in the quality of infant-adult relationships. Reprinted from: CHILD DEVELOPMENT, 1978, 49, 483-494.