Several studies have shown that women have to meet more / higher criteria to be judged as very competent and possessing leadership ability than men. Once women have obtained a position of leadership, their qualifications are rated as less, even if they have performed the same as men. These two forms of prejudice stem from a perceived contradiction between typical female traits (e.g. caring and helpful) and leadership traits (e.g. assertive and independent). For more background information read the entire article here.