On average, intersexes have IQ scores in the 110 to 125 range, well above the mean for the population

(Dalton, 1968; Ehrhardt & Money, 1967; Lewis, Money, & Epstein, 1968). One possible interpretation is that a hormonal pattern intermediate between male and female promotes great intellectual development. Another possibility is that intersexuality may be more common in intelligent families than in less intelligent ones or that the more intelligent families are more likely to bring their intersexed children to an investigator’s attention. What kind of study would be best for deciding among these hypotheses? (For one answer, see Money & Lewis, 1966.)