The percentage of paying social game players in the U.S. has nearly doubled, but those gains have been offset by users spending less on social games, particularly on farming titles, according to a new study. Analyst firm SuperData says that the average revenue per paying user (ARPPU) for farming titles has fallen in recent months, while the ARPPU for "mid-core" games is the highest out of all social game categories. Mid-core games are titles that target core audiences, such as strategy or combat-focused releases (e.g. Empires & Allies, Social Empires), but feature free-to-play business models. Mid-core players are currently spending over three times more than social farm game players. SuperData claims that ARRPU in general has fallen by around $8, from $45.58 in April 2011 to $37.59 last month. This amount seems to fluctuate significantly from month-to-month, though, as it was $46.71 in March 2012. Despite the drop in ARRPU, social games are attracting more paid users. SuperData notes that social games converted 2.5 percent of players into spending users in April, compared to only 1.4 percent during the same period last year. The group also predicts that by 2015, the worldwide social game market, including the mobile sector, will reach $13 billion. It currently estimates North America's revenues for 2012 at $1.8 billion, and Europe's at $1.4 billion.