This is has been sitting around in the draft bin for too long: Study: P2P effect on legal music sales “not statistically distinguishable from zero”
“A new study in the Journal of Political Economy by Felix Oberholzer-Gee and Koleman Strumpf has found that illegal music downloads have had no noticeable effects on the sale of music, contrary to the claims of the recording industry.”
Great news. Music sales go up and down because demand goes up and down, quality goes up and down, the economy and affordability and attractiveness of music varies.