Server Type Preference
There are 3 main server types in current MMOs - PvE, PvP, and RP. The following are demographic and motivational differences among players with regard to server type preference. I was most interested in the differences between PvE and PvP servers.
Overall, players who prefer PvE servers are disproportionately more likely to be female while players who prefer PvP servers are disproportionately more likely to be male. There is also a substantial correlation with age - younger players prefer PvP servers (r = .28). A multiple regression showed that the Competition and Mechanics (min-maxing) motivations are the best predictors for PvP server preference (r-squared = .32), as would be expected. Together, this suggests that players on PvP servers tend to have a higher proportion of male players and also tend to consist of younger players.
This has an interesting effect on gender-bending rates. The higher proportion of male players increases the chances that a female avatar is being played by a male players. On a normal WoW server where about 85% of players are male, there is a 50% chance that a female player is being played by a male player. If we assume that 90% of players are male on a PvP servers, there is an estimated 68% chance (about 2/3) that a female avatar is being played by a male player.
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With regard to preference for RP servers, there are no overall gender differences. Men and women are equally likely to choose an RP server if it existed for their game. Age isn't correlated with RP server preference (r = .02). Unsurprisingly, a multiple regression showed that the Role-Playing motivation is the best predictor for RP server preference (r-squared = .37). So unlike PvP server preference, there are no demographic differences for RP server preference.