Based on the results of its annual "Core Gaming" survey, the NPD Group claims that there are 34 million "core gamers" in the United States who are spending an average of 22 hours per week playing games, down from the 37.5 million "core gamers" the firm reported last year.NPD Group analysts surveyed 7,927 U.S. citizens ages nine and up last March to learn more about their video game playing and, specifically, what the habits of "core gamers" were in 2014. They defined a "core gamer" as someone who plays specific genres of games (basically, anything that's not a puzzle game) on PCs or non-Nintendo home consoles an average of five hours or more per week.The firm also claims that only 26 percent of those surveyed preferred to buy digital copies of games rather than physical if the price was the same. That's actually a modest increase over last year, in which only 21 percent of those surveyed expressed a preference for buying digital.A sample of the report is available on the NPD Group website, though you have to provide your contact information to get it.