Sibsize, family environment, cognitive performance, and affective characteristics.
The study examined to what extent relationships between sibsize and the cognitive and affective chaarcteristics of children were mediated by family environments. The Alice Heim nonverbal intelligence test (AH4), the Watts Vernon English test, and the Vernon graded mathematics test were used to assess the cognitive performance of 15-year-old children (383 boys and 396 girls). The Ss formed part of a longitudinal national study of English school children. Also schedules were administered to measure children's educational and occupational aspirations, self-concepts, and attitudes toward school. From parental interviews a family environment index consisting of both distal and proximal measures was constructed. The Jackknife technique was used in the analysis to adjust significance levels. Regression surface analysis indicated that at each environment level, sibsize was related only to the English achievement of girls and boys and to the aspirations of girls. However, the shapes of the surfaces suggest that if parents create differential learning environments for different siblings then the behaviors of the siblings are likely to vary, which provides tentative support for the confluence model of sibsize influences on the behaviors of children.