A recent report has confirmed what many of us suspected all along — it just doesn't pay to be nice, particularly at work. In a study to be published in The Journal of Personality and Social Psychology, researchers found that people who are aggressive, outspoken, and willing to be disagreeable make significantly more money than their nicer coworkers. Do companies unwittingly reward bad behavior, or are nice people simply unwilling to negotiate better salaries? Here, a brief guide:

What did the researchers survey?
They analyzed almost 20 years of data from three different surveys, which sampled about 10,000 workers in a wide range of professions, salaries, and ages. The surveys looked at factors like agreeableness, cooperation, kindness, and other psychological factors.

What did the study reveal?
"Nice guys are getting the shaft," says study co-author Beth A. Livingston of Cornell University's School of Industrial and Labor Relations, as quoted in The Wall Street Journal. Men who were below average in terms of agreeableness and cooperativeness made 18 percent more — almost $10,000 more per year — than their kinder, gentler office mates. Similar, though less striking, results were found for women judged less agreeable; they made almost $2,000 more per year than their more charming counterparts.

Does this affect hiring practices?
Possibly. In a separate survey, the researchers asked 460 business students to act as hiring managers for a fictional company. After examining descriptions of job applicants, men who were deemed highly agreeable were less likely to get the job. "Niceness may not fit social expectations of 'masculine behavior,'" says Adriana Barton in The Globe and Mail.

What does this reveal about salary negotiations?
It pays to speak up: People interested in being well-liked usually won’t play hardball in salary talks. "I think people have to be assertive," says researcher Tim Judge, as quoted in the New York Daily News. "Pay is not solely determined by your qualifications or economic factors. If leaders get the performance that they expect, we employees get the pay for which we ask."

Why the difference between men and women?
Cultural norms, in most cases. "People interpret disagreeable behavior by men and women differently," says Judge, as quoted by ABCNews.com. "Disagreeable men are [seen as] tough-minded and good negotiators. Disagreeable women are seen as "bit**es."

So should I start acting more obnoxious at work?
That could backfire. Other studies have shown that cooperation is a valued skill in many workplaces, and pushy behavior is not uniformly rewarded. People who are too aggressive are "setting themselves up to be fired," says psychologist Joshua Klapow. "This study has potential to drive people to act in an unproductive way."

Sources: ABCNews.com, Globe and Mail, New York Daily News, TIME, Wall Street Journal