"GAO did not have sufficient information to determine the extent to which these gender-related price differences were due to gender bias as opposed to other factors, such as different advertising costs," researchers concluded.
The GAO also reviewed academic studies on whether women paid more for mortgages, small business credit, auto purchases and auto repairs, but could not reach any definitive conclusions because of conflicting results and the age of some of the studies.
The report noted that some state and local governments have passed laws or ordinances to prohibit businesses from charging different prices for the same or similar goods or services.
One of those is New York City. And Casey and Maloney, in their letter to the GAO, cited a Dec. 2015 study by the New York City Department of Consumer Affairs that compared prices of about 800 products that had different versions marketed to men and women but were "substantially similar" except for packaging. That study found that, on average, women's products cost 7 percent more than products marketed to men.