The study in question puts some interesting numbers on the effect of not studying on grades:
At Berea, those students whose (randomly selected) roommates had video games earned significantly lower first-semester GPAs: for males, 2.74 vs. 2.98; for females, 3.03 vs. 3.16. Students with a roommate who brought a video game to college report playing video games 4.06 hours per week; students with roommates who did not bring a video game report spending 0.79 hours per week. The first group spent 2.9 hours a day studying; the second group reports spending 3.6 hours a day studying.
So, on average, a video game-owning roommate knocks the average student’s grades down .24. Still, more than three hours of video gaming only reduces studying by .7 hours.
I’m curious, though — in addition to the hours the subjects spent playing, the roommates’ playing might be distracting. Not to mention that video game-owning roommates might, disproportionately, be distracting in other ways; they might be less serious in general.