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makingmusic476 said:
I'm often having to defend this site on other forums like HighDefDigest.com, and I find myself often having trouble doing so, because, to be honest, I'm not really sure what methods are used by ioi/TheSource.

From the way I understand things, ioi and TheSource estimate the American weekly numbers, and update them to coincide with NPD at the end of each month. For Japan and the EU, they use GFK, Media-Create, Famitsu, etc.

However, I tried to argue this point with someone at HDD, and they said that the ps3 figures for VGChartz were off by over 500,000 compared to the NPD tracking thread on NeoGAF. (This was over a month ago, so I'm not sure how holiday weekly sales could've factored in to this.) I tried to find this thread on NeoGAF, but couldn't, and I had a hard time debating this person without too much concrete information.

Anywho, I keep hearing talks of a "methodology page" on here. Could someone give me a link? It would be really helpful when defending this place on other websites.

 Actually he does it the same way NPD does, through extrapolation of numbers by sales reports he gets from a number of stores.  Which obviously have to stay secret otherwise pressure would be applied by "competeing" companies who would perfer there not be a free option out there that gives pretty accurate numbers.

Then adjustments are made to the totals when additional data comes in that shows the data is off.  The biggest of these is shipping numbers that are released quarterly by making an educated guess about how many of the shipped products are in the retail channel, and other reports being ones from NPD, Charttrack, Medicrate Famitsu etc..

Of atleast that's my understanding of it.