A recent  study has found that male stock analysts tend to be biased toward public companies headed by men as opposed to women, according to a recent article in The Wall Street Journal. The article says that this group bias leads to a boost in share prices of firms that they don’t favor—that is, because they typically underestimate performance of female CEOs, an earnings surprise from such a firm often leads to a boost in share price.

The study, conducted by researchers at the University of Miami School of Business Administration, states that these findings extend to stock analysts’ buy and sell recommendations, “with systematically more buy than sell recommendations for stocks of firms headed by CEOs belonging to their in-group.” Specifically, the report shows that the percentage of buys and strong buys for companies led by women “is lower by 4.21 points, and for sells on female-led companies it is 2.50 points higher.” Female analysts, on the other hand, were found to be less biased against male-run companies.

The explanation? The study states that “in-group bias is one of the main aspects of human behavior” and is attributed in part to genetics, and “a need to reinforce social identity.”