Mental abilities: sibling constellation and social class correlates.

Verbal number reasoning and spatial ability scores were obtained for 185 11 year old boys. The relations between the mental abilities social status characteristics and sibling constellation variables were examined using a series of multiple regression equations. A 3 term equation including fathers occupation status inverse of the number of children in the family and the product of the 2 variables parsimoniously accounts for as much significant variance in the data as complex many-termed equations. Birth order crowding ratio their squares and products provide no better prediction beyond that afforded by the 3 term equation. The constellation variable inverse of sibsize is strongly associated with higher verbal and number ability scores of boys in families of low socioeconomic status but the effect is attenuated in families of higher socioeconomic status. The results suggest that birth order may be a superfluous sibling constellation variable in research but that the inclusion of the variable inverse of sibsize may lead to a greater understanding of the relationship between social status and mental ability performance. (authors modified)