Although women now attend college at a higher rate than men, and have for the most part closed the gap in achieving advanced and professional degrees, women are not occupying the real power positions in corporations, academia, or the professions in anywhere near the same proportions as men. Catalyst, among many other organizations, bemoans this reality. The fact of the underrepresentation of women at the top begs the question of why. One part of the answer is women’s reluctance to embrace power.

The evidence shows that women are less power-oriented than men. Women have more negative attitudes toward holding power, they are less likely to pursue power-based influence strategies, they are more bothered by and disfavor hierarchical relationships, they are less motivated to dominate others, and they are less likely to take actions to attain power. Moreover, in situations such as salary negotiations, studies show that women often believe that they deserve less than similarly qualified men and are, as a consequence, likely to demand less and to press their salary demands with less vigor. (On this last point, also see this pdf.)

Women bank too much on likeability. To be sure, people in general overestimate the importance to their influence of being well-liked, and underestimate the effectiveness of displaying anger, but women seem to be more susceptible to these beliefs than men. And while men, too, are sometimes uncomfortable with the actions required to attain power — building relationships with useful others, displaying confidence, engaging in self-promotion, being willing to work long hours — women, as a rule, tend to be less willing to make the trade-offs required to attain positions of power. As a consequence, many women, including talented graduates of MBA programs, reach a point several years into their careers where they decide the compromise isn’t worth it, and drop out of the quest for power.

Two implications follow.

First, women must make more of what they see as trade-offs. Everyone, men and women, must make certain sacrifices to achieve power and career success. If women want to achieve power at the same rate as men, they will need to be willing to make difficult choices, whether by forgoing family for work or choosing a partner in part on the basis of whether that individual will be supportive of their power quest (“strategic marriage,” as a former student of mine put it).

Second, women need to get tougher. It’s true that women tend to be perceived more negatively and be less liked when they use the same power strategies as men. (This is an unfair reality that Alice Eagly has referred to as “the double bind.”) But there is little evidence to suggest that those strategies aren’t just as effective for women. Carly Fiorina reached the CEO position at Hewlett-Packard because throughout her career, she was willing to market herself. Although Meg Whitman at eBay presents a kinder exterior image, people who crossed her suffered consequences. No one who witnessed former British Prime Minister Margaret Thatcher aggressively holding her own in a media interview could doubt her confidence and refusal to back down from a conflict — or could question where her nickname, “the Iron Lady,” came from.

Although we might wish that the rules for attaining power were different, or different for women, they aren’t. There’s no question that women are as qualified as men to hold positions of power. I would argue that we need them to do so. The question is: when will they step up to the pursuit of power, vigorously and strategically?

Jeffrey Pfeffer is the Thomas D. Dee II Professor of Organizational Behavior at the Graduate School of Business, Stanford University, where he has taught since 1979. His forthcoming book from HarperBusiness is Power: Why Some People Have It and Others Don’t.