They spend 29 hours a week in virtual world compared to 25 hours for males.
"The women play more intensely than the guys do. They're less likely to quit, and they're happier playing," said Williams.
However, they still underestimated their playing time more than men.
The study showed that the top 10 percent of female players averaged nearly 57 hours per week, eight more than male players.
Contrary to another stereotype - that of the teenage game player - the average age of the 7,000 players surveyed was 31.
"We found that older players were more typical," said Williams.
There were more players in their 30s than in their 20s, and playing time tended to increase with age.