Statistical analysis is also performed to identify test items for which subgroups of the population may perform differently. For example, on biology tests, it was discovered that women generally performed better on questions concerning the reproductive system. Those which show a large differential factor of 15 percent or more are reviewed and sometimes discarded. Surprisingly, some of those items with a high DIF are standard physics problems in kinematics, electrostatics, or optics, with no obvious pattern in terms of content or skill levels to explain the wide differentials. A joint study by the ETS and the College Board concluded that multiple choice formats favor men over women, partly because men are more willing to guess on tests when they don't know the answer.
Men also perform better on timed tests.
Another ETS study found that when the time limit was removed from SAT subtests, girls' scores improved markedly, while boys' scores changed very little. At present, there are no plans to alter the format of the tests. According to Zappardino, gender differences can certainly be manipulated by selected different test items. For example, for the first several years when the SAT was offered, boys scored higher than girls on the math section, while girls achieved higher scores on the verbal section. The ETS decided the verbal test needed to be balanced more in favor of boys, and added more questions pertaining to politics, business and sports.