Why do so few women occupy positions of power and prestige? Virginia Valian uses concepts and data from psychology, sociology, economics, and biology to explain the disparity in the professional advancement of men and women. According to Valian, men and women alike have implicit hypotheses about gender differences - gender schemas - that create small sex differences in characteristics, behaviors, perceptions, and evaluations of men and women. Those small imbalances accumulate to advantage men and disadvantage women.