A study that compared states that ban asking about pay history at job interviews to those that don't found that when what a job candidate made before is no longer a question, that person's pay increases, an effect that was found to especially benefit women and African-Americans, said the Wall Street Journal.

Overall, the study's researchers at Boston University found that in states that ban questions about past compensation, wages for job-switchers in general went up by about 5 percent. In the case of African-American job candidates, this pay increase was 13 percent, while for female job candidates it was 9 percent. The researchers believe this differential arises because when employers cannot ask about what applicants made at their previous jobs, employers cannot use past salaries as the base rate for the hirees' new salaries.

Other studies have found, however, that being open about current pay can be a good way to close further wage disparities. One academic study involved looking at a company with almost 9,000 employees, specifically its performance-based rewards decisions after management adopted a set of organizational procedures, including transparency, into the company’s performance-reward system. The study concluded that transparency does, to some extent, close compensation gaps in this area.