With virtual goods becoming the main driving force of the games industry , some interesting figures have been thrown up by a survey of US gamers carried by market research firm VGMarket for global payments outfit PlaySpan, part of Visa.Of the 1,000 respondents, 31 percent said they had used real-world money to purchase virtual content, with 57 percent of these making purchases at least once a month.More notable though was the gender split. Across both MMOGs and casual games, women said they spent significantly more on virtual goods than men.For some reason, the survey splits games into first and thirdparty categories, with women, on average, saying they spent $111 a year in thirdparty MMOGs and $62 in thirdparty casual games.The comparative figures for men were $74 and $28 respectively.Also significant was the change in terms of absolute money spent on free-to-play games compared to 2010's survey.When it came to more hardcore games, such as MMOGs and console/PC titles, the average spend was up 20 to 90 percent year-on-year, depending on category.However, when it came to casual games, average spend was down in all categories, by between 20 to 60 percent.Confusingly, this decline didn't seem to be reflected in the survey's other data. For example, all types of virtual content (except virtual gifts, down from $30 to $23), experienced an increase in average spend year-on-year.Of course, it's likely these sort of surveys aren't as statistically rigorous as they might be, plus the results are based on respondents' choices about what they thought they spent rather than actual spending patterns.And, clearly, it's not the same set of respondents year-on-year either.For the record, the survey was carried out in July with 1,006 US gamers aged 13 to 65, with an average age of 25 years. 72 percent were male. The average household income was $68,897.You can download the complete survey here (email registration required)