Birth Order, Income, Sex, and School Related Attitudes.
Birth order was used to predict grades and school related attitudes following Bradley’s hypothesis that first-borns are more academically interested and less socially interested than later borns. Income, sex of child, and size of family were studied as interacting variables. Several interaction effects were found in the absence of birth order main effects which indicate a need to study birth order as an interacting variable rather than as a single independent variable.