NPD is a reliable source.
But look at the worldwide breakdowns:
Wii gets ~35-40% of sales from the Americas.
360 gets ~60-65% of sales from the Americas.
PS3 gets ~40-45% of sales from the Americas.
That means for July the 'discrpency between professional tracking agencies' breaks down like this:
PS3 was 3% different from NPD. .40 x .03 = 1.2% difference - not worth changing given NPD's sampling has roughly 3-5% margin of error by my estimates. Overall - this is a 7k/4200k difference! Not a big deal (1/10 of 1% adjustment if it was adjusted for overall totals).
For simplicity, say Wii was 21% different from NPD in July. .21 x 3/8 = 7.875% difference. Might be worth bumping up a bit, but the figures are still very close worldwide 85k/10570k (8/10 of 1% adjustment if it was adjusted for overall totals)
360 - .26 x .625 = 16.25%. Again, the totals are close worldwide 47k/10520k (4/10 of 1% adjustment if it was adjusted for overall totals)
In other words, there may not be a need for a bump if ioi sees it as I do.
People are difficult to govern because they have too much knowledge.
When there are more laws, there are more criminals.
- Lao Tzu
