Because autism is at least three times as common in boys as in girls, scientists routinely include only boys in their research. The result is that we know shockingly little about whether and how autism might be different in girls and boys.
What we do know is grim: On average, girls who have mild symptoms of autism are diagnosed two years later than boys. There’s some debate about why this might be so. From the start, girls’ restricted interests seem more socially acceptable—dolls or books, perhaps, rather than train schedules—and may go unnoticed. But the fact that diagnostic tests are based on observations of boys with autism almost certainly contributes to errors and delays.
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