Brizendine explains: "It has been my observation that, in a social setting, girls speak two or three times more words per day than boys." This observation is also "echoed," she says, by a study that found "young girls speak earlier and by the age of 20 months have double or triple the number of words in their vocabularies" compared with boys. But that study, by psychologist Janet Hyde, looks at a different age group and a different measure. "Brizendine is not careful about the scientific data," Hyde told me. A larger vocabulary at an early age could reflect an earlier maturation for girls. The evidence does not suggest that adult women have double the vocabulary of adult men, says Hyde. Rather, the data show that differences in adults are small.