“Common sense is, or should be, the handmaiden of economic analysis. When given the choice of free and convenient high-quality copies versus purchased originals, is it really a surprise that a significant number of individuals will choose to substitute the free copy for the purchase?”
By 2007 CD sales were already on the way out. I’m not sure any study has separated the effects of file sharing from the effects of a format shift.
This may be a fun academic exercise, but it feels like fighting the last war.