A January, 2016 working paper from a doctoral student at Queens’ University in Canada suggests that pirate downloads can help increase sales as much as substitute them. The paper establish a link between pirated downloads on a torrent tracker and album sales.
The research tracked downloads of 2,251 albums over half a year and correlate downloads on the tracker with album sales in the US.
The hypothesis is that albums that were heavily downloaded might see lower sales because of a higher availability in file sharing networks - or that they might see higher sales because of a “word of mouth” effect.
The analysis found that an increase in album downloads correlated to a drop of (just) 0.17% in physical album sales but a 0.21% increase in digital sales and concludes “… file sharing activity has a statistically significant but economically modest negative effect on legitimate music sales”.