Academic research on gender and negotiation suggests that part of the unexplained gap may be tied, at least in part, to the negotiating process itself. It may be that some women have lower pay expectations. Men, on the other hand, have been found to be more likely to negotiate higher starting salaries.

The work by Ms. Riley Bowles and her peers suggests that women in the work force can use specific advice. Here are some of their suggestions:

BE PROACTIVE If you believe you deserve a raise, don’t sit around and wait for someone to notice. “A lot of women, and this is quite commonly found, think, ‘As long as I work really, really hard, someone will notice and they will pay me more,’ ” said Karen J. Pine, a psychology professor at the University of Hertfordshire in Britain and co-author of “Sheconomics” (Headline Publishing Group, 2009). But “people don’t come and notice.”

You also want to think about the best time to approach your boss. It may make sense to approach him or her after an annual performance review, said Evelyn F. Murphy, president of the WAGE Project, a nonprofit organization, who runs negotiation seminars for women. “Or, if you just took on a major responsibility or won an award.”

BE PREPARED Doing your research pays, literally. A study found that men and women who recently earned a master’s degree in business negotiated similar salaries when they had clear information about how much to ask for.

But in industries where salary standards were ambiguous, women accepted pay that was 10 percent lower, on average, than men. “In our experiments, we found that with ambiguous information, women set less ambitious goals,” said Ms. Riley Bowles, who ran the study. “They asked for less in a competitive negotiation and got less.”

That theory also holds in other areas where there aren’t set expectations, like executive bonuses and stock options. “You get bigger gender gaps in those less standard forms of pay,” she added.

That’s why you need to be prepared. Informational Web sites like Payscale.com and Salary.com can help uncover what people are being paid for a particular position in your geographic area. And Glassdoor.com and Vault.com provide intelligence on pay inside a company — employees share their salaries online.