I find it more likely that good songs are both pirated more and bought more, rather than that the piracy increases the sales. Correlation, not causation.
From the paper, which apparently nobody here actually bothered to skim:
> To study this phenomenon, I must overcome the fact that file sharing is endogenous in its determination of an album’s sales because an album that is popular in file-sharing networks will also be popular in retail markets. This occurs because file-sharing and retail demand are both driven by unobserved album quality. To address this endogeneity, I exploit exogenous variation inhow widely available an album was prior to its official release date. An album’s ease of availability in file-sharing networks is positively correlated with the number of times that it is downloaded because availability determines the supply of the album in file-sharing networks. Availability is not independently correlated with an album’s popularity in retail markets because pre-release filesharing is driven by leaks, which are “crimes of opportunity” that occur at some stage of the production or album marketing process (Williams, 2009).
