Yeah, I should clarify that I meant you could do it if you control whether they're released under DRM or not. If a group of indie developers wanted to pool together and run an experiment, they could do it in a way that was really informative about its effect on revenues (the conclusions might not hold up if you tried to extrapolate too far beyond indie games though).
I agree that the existing data aren't much like the random experiment I was talking about.
Maybe, but what if indie games are less susceptible to piracy than blockbuster games.
There are really just massive statistical hurdles to overcome with this type of analysis.
You could prove that indie games with strict DRM will perform differently than indie games without strict DRM, but extrapolating that to feature, blockbuster games is problematic.
I agree that the existing data aren't much like the random experiment I was talking about.