Data from Sexual Experiences of Adolescents with Low Cognitive Abilities in the U.S. What's the reason for these results? I think one of the simple ones (though not the only one) might be a form of positive assortative mating: like with like. If you assume that affinity is proportional to cognitive similarity than the sample of individuals for someone who has an IQ of 100 vs. 130 or 70 is far higher for any given range. For example, nearly 2/3 of individuals on the frequency distribution lay within 1 standar deviation of someone with an IQ of 100. In contrast, only around 1/7 of the population is within 1 standard deviation of someone at 130 or 70.