scottie on 21 December 2008
It depends what you are looking for
Wikipedia is actually the main authority on shipment figures
Pretty much each individual country has an equivalent of NPD, and generally these are seen as more accurate and more reliable, but they track on a month by month basis, instead of week by week. And recently VGChartz has started taking larger sampling sizes, and possibly improved their calculating abilities, leading to greater accuracy. We rarely disagree with NPD nowadays
But VGChartz is essentially the only place to find statistics for worldwide sales, and weekly sales, so in some senses we are the main authority, and we have been cited by mainstream media many times, see this thread for a list
http://vgchartz.com/forum/thread.php?id=17185
