Abstract
Regression surface analysis was used to examine the confluence model which proposes that the relations between birth order and intellectual ability are accounted for by the age spacing between adjacent siblings. The model was extended to investigate relationships between birth order, age spacing between older and younger adjacent siblings, and measures of intelligence, mathematics, word knowledge, word comprehension, the language environment of the family, and parents' expectations for 500 11-yr.-old Australian children. The results provided support for the confluence model when relations between birth order, age spacing to younger adjacent siblings, and intelligence test scores were investigated but in general the propositions of the confluence model were not supported when the academic achievement and family environment scores were examined.
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