determine whether or not an adult exhibits symptoms of autism. The AQ has subsequently been used in hundreds of studies including one study of half a million people, showing robust sex differences and higher scores in those who work in STEM. Prenatal neuroendocrinology Baron-Cohen's work in E-S theory led him to investigate whether higher levels of prenatal testosterone explain the increased rate of autism among males. His prenatal sex steroid theory of autism gained additional support in 2015 and 2019 in finding elevated prenatal androgens estrogens are associated with autism. In his 2004 book Prenatal Testosterone in Mind (MIT Press) Baron-Cohen put forward the prenatal sex steroid theory of autism. He proposed this theory to understand why autism is more common in males. Using the Cambridge Child Development Project that he established in 1997, a longitudinal study studying children of 600 women who had undergone amniocentesis in pregnancy, he followed these children postnatally. This study demonstrated, for the first time in humans, how normative variation in amniotic prenatal testosterone levels correlates with individual differences in typical postnatal brain and behavioral development. His team discovered that in typical children, amount of eye contact, rate of vocabulary development, quality of social relationships, theory of mind performance, and scores on the empathy quotient are all inversely correlated with prenatal testosterone levels. In contrast, he found that scores on the embedded figures test (of attention to detail), on the systemizing quotient (SQ), measures of narrow interests, and number of autistic traits are positively correlated with prenatal testosterone levels. Within this study his team conducted the first human neuroimaging studies of brain grey matter regional volumes and brain activity associated with prenatal testosterone. Other clues for the theory came from Baron-Cohen's postnatal hormonal studies which found that autistic adults have elevated circulating androgens in serum and that the autistic brain in women is ‘masculinized’ in both grey and white matter brain volume. An independent animal model by Xu et al. (2015, Physiology and Behavior, 138, 13–20) showed that elevated prenatal testosterone during pregnancy leads to reduced social interest in the offspring. Baron-Cohen's group also studied the rate of autism in offspring of mothers with polycystic ovary syndrome (PCOS), a medical condition caused by elevated prenatal testosterone. He found that in women with PCOS, the odds of having a child with autism are significantly increased. This has been replicated in three other countries (Sweden, Finland, and