Four out of 10 of those who have played an upgradable freemium game report making an in-game payment to extend or enhance a game, according to The NPD Group's Insights into the Freemium Games Market study.

Freemium games are digital games that are free of charge to play, though some may offer upgrades such as advanced features, functionality or new content that require additional payment.

Among freemium gamers, females are significantly more likely than males to have played a freemium game, but females are less likely to pay for an upgrade.

"The majority of freemium gamers who opt to pay to upgrade their experience do so within the first month of playing a particular game," says Anita Frazier, industry analyst, The NPD Group. "When designing a game, it's important to consider features that would drive quick conversion to pay."

With no barrier to entry other than ownership of a compatible device and access to the Internet, adoption of freemium games is quite high among those who are aware, with only 15 percent of gamers who are aware of freemium games choosing not to play them. Freemium gaming is also quite "sticky," with a conversion rate of 84 percent that continue to play among trial users. Females are more likely to convert than males, while males and those ages 13-34 are more likely to abandon freemium gaming after trying it.

"Males and those ages 18-34 are traditionally seen as a big part of the core gamer audience, so it's likely these groups are not quite as engaged with freemium because the gaming experience is quite different from what they are used to from the games they play on consoles, handhelds or PC's," says Frazier. "At a minimum, for these gamers a freemium game would provide a different experience, like a snack versus a full meal."

High awareness, high trial and high adoption of freemium games results in about 38 percent of the U.S. population ages 2 and older currently playing some type of freemium game.

*Data was collected via an online survey from Feb. 27-March 7. The survey was completed by 6,416 individuals ages 2 and older. In cases where surrogate reporting was used, mothers were asked to bring the child to the computer to answer survey questions, either with or without assistance. In order to qualify as a gamer, respondents had to report that they currently and personally play video games. Final survey data was weighted to represent the U.S. population of individuals ages 2-99.