As a followup to my local data breakdown, I thought I’d link to some other interesting findings:
Added 17/11/09: Marketing influences games more than ratings
A study from 2006 that concludes no correlation between sales & score.
This compares metacritic rating to overall sales for 1281 games during the PS2 era.
Some data extracted from between March 2007 & March 2008
A more recent study from May 2009.