We love sales data. We regularly cite NPD Group, Chart Track, Enterbrain and Media Create figures, but rarely, if ever put stock in amateur sales estimation outlet VGChartz. It's not just our aversion to plurals that end with Z, it's that the methodology, the educated guesses that lead the site to conclude that, say, Metal Gear Solid 4 sold 1.3 million copies on day one, don't instill much confidence.
Gamasutra's Simon Carless peeks into the VGChartz methodology and the validity of its weekly published video game sales estimates. In short, his findings point to some noticeably large variations between VGC's guesstimates and more trusted outlets like NPD, to which many publishers subscribe.
We agree with Carless that a community driven resource for estimations is a good idea, but we're not particularly fond of the accuracy that VGC offers. For those passionate about sales data, it's a good read.