Leadership is the process where a person exerts influence over others to achieve goals. Effective leadership increases a firm's ability to meet new challenges. Leadership styles may vary across cultures. For example, European managers tend to be more people-oriented than American or Japanese managers. Various power bases enable managers to influence subordinates, including reward, coercive, legitimate, expert, and referent power. The number of women managers is rising but still relatively low in top levels due to stereotypes. However, research shows there are no actual gender differences in leadership effectiveness.