How does vgchartz get its data?

[gipsy_jack]

ioi said:

gipsy_jack said:

I think vg chartz underestimate the psp Sells.

For example polyphonie claims that they allready selled fast 2 million Gran turismo portable and VG chartz says only 1.200.000.

How possible is it?

Retail sales + PSN downloads (Polyphony) vs just retail sales (VGChartz).

Same with GT5 prologue.

Ah ok.

But why can't they have the PSN sales?