The NPD has revealed early fruit of its recently-announced intention to look more closely at digital game revenues.
Its Game Purchase Drivers 2010 report found that an average of 71 per cent of US game purchases over the last three months were physical.
Of the 29 per cent that were digital, 42 per cent were via mobile app stores or phone carriers - thus constituting some 12 per cent of total game sales.
30 per cent of the digital sales were via "console/portable services such as Xbox Live or PlayStation Network." This extrapolates to 8.7 per cent of all game sales.
Game download portals such as Steam and BigFishGames were named the largest driver of digital sales, constituting 47 per cent. This equates to 13.63 of combined physical and digital sales for the period.
The NPD also claimed that around 20 per cent of the digital consumers had purchased add-on DLC in some form.
Of the total sales for the three months, 10 per cent of purchasers had done so with the help of trade-in games. The average number of games (again, physical and digital) bought over the period was 3.1.
The study polled 3704 Americans online, with results adjusted "to be representative of the U.S. population age 2+."