http://forum.beyond3d.com/showthread.php?t=46474

Maybe some of the more knowledgable members here should add to that thread, answering stuff like "Vgcharts esitimates comes from bad guess work and then looking at NPD numbers and correct their guesses."

In short though.  It doesn't come from guesswork but statistical sampling.  Sometimes the site does adjust for other sources, but it's fairly rare.

Software can be off because, well

A) it's hard to track the holidays 

B) It's harder to track software with a smaller sample size.

One other thing to consider is that having more data isn't going to always lead to most accurate results.

Look at Famitsu and Mediacrate who both have around the same percentage of the market.  They can drastically disagree with each other by extreme amounts.

Here, yes. But not over there, right?

Interesting, I use this post like a reminder of this thread ( with the link to Beyond 3D ) so I can read it later ( now I'm going to work ).

The posters on that site haven't been paying attention to the data, they say VGC is off of Europena data, but aren't the gfk and chartrack data pretty much the same as VGC?

The same old misinformation. Luckily it's getting less and less common all the time.

this kind of misinformation is going to continue for quite some time, no matter what you tell certain people..

@Avinash: There were situations when European numbers (for a specific country) were far off. Ioi estimated Germany's sales after PS3 price drop to about half of what GFK estimated. Recently there was a correction to France numbers (around 130k off for PS3 lifetime compared to FGK). I think that there were also correction's for Italy and Spain eariler but I don't remember if they were big.
It is also important that we don't get GFK numbers often, so there aren't that many chances to correct numers.

I think that UK numberes are good and don't remember any correction to them.

Yeah but those are individual instances where the data is off and when it is changes are made, but its not like they are continuously off  (we'll know for sure when the financial data comes out for Q3)

Well if those anti-VGChartz would just come and check the site out for themselves and actually read that ioi stated more and more times that he receives samples and those samples are getting larger as months go on. Then they would actually understand what VGChartz is doing.