A retrospective study of 146 pairs of twins was performed. The twin pairs each had one male child and one female child. Their birth weights were studied to determine if the male twin was consistently heavier. The difference in weights was calculated by subtracting the female weight (in ounces) from the male weight (in ounces): d = Im - Of After looking at 146 pairs of twins, the study finds the 90% confidence interval for the mean difference of weights (in ounces) is: 0.4 E+ E A