Since Daniel Goleman‘s Emotional Intelligence, we’ve recognized the importance of tuning into social and emotional factors in the workplace. But many popular depictions of the workplace don’t show any evidence of that sensitivity. Mad Men, Wall Street, and others impress that in business, only the strong survive.

But emotional intelligence implies that successful leaders should be nice. And while being nice may have social benefits, does it pay?

The key is in how agreeable you are. Timothy Judge, Beth Livingston, and Charlice Hurst examined this trait in a paper [PDF] in the Journal of Personality and Social Psychology this year. By way of background, conventional personality research defines agreeableness as two related qualities: (1) the extent to which you value getting along with others, and (2) the degree to which you are willing to be critical of others.

Using earnings data, the researchers found that men who rank high in agreeableness make substantially less than men who are less agreeable. Across studies, this difference was as high as $10,000 per year. Conversely, women’s earnings were less affected. There was only a small earnings difference between women high and low in agreeableness, and it was often not statistically reliable.

So, why do these results differ for men and women? And why do nice guys finish last?

There is a stereotype that when men lead, they make decisions without concern for what other people think. Indeed, a final study in this same paper asked people to evaluate potential leadership candidates. Agreeable men were rated least attractive as potential leaders.

And as for nice guys (and to a lesser extent, nice women) finishing last, let’s recall the two related qualities of agreeableness. Concerning a value for getting along, career advancement requires a willingness to ruffle feathers from time to time. Good leaders need to be able to tell people things that they do not want to hear. And honestly, putting yourself forward for a promotion means putting yourself before others.

Career success also involves being critical. While some managers may want to surround themselves with people who obediently agree, most want those who will find the flaws in a plan before it is implemented. Less agreeable people are prone to give this kind of criticism.

Of course, this is not license to be a jerk at work. The data also suggest that people lacking agreeableness are more likely to lose their jobs than agreeable ones. There is a big difference between being disagreeable and being unpleasant.

So, what can you do, whether you’re more agreeable or not?

First, get to know yourself. There are plenty of quizzes out there to measure the “Big Five” personality dimensions. Find one, take it, and get an objective sense of how agreeable you are.

If you are more agreeable, go out of your way to find the flaws in plans that you hear. Put aside your personal relationships and think about what can go wrong. It helps to imagine that the idea is going to be implemented by another company, to help separate the people from the ideas. Next, find ways to express your concerns. People can be upset with you for a day if they recognize the long-term value of your advice. Express your concerns with empathy, but directly. Try practicing giving negative feedback with a friend first, before doing it for real.

If you are more disagreeable, balance criticism with empathy. Remember that it is difficult to hear criticism of your ideas and your performance. You can be firm while still recognizing the impact of your message. If you think you’re developing a reputation for being unsympathetic, practice giving bad news to a friend. Find out which parts of your delivery are causing people to bristle. A strong leader can guide without being mean.

Nice or not, without a doubt you can still be a great leader — you just have to adjust your strategy.