Michael Geist sez,
The NPD Group response contains math errors for both non-P2P users (the total should be $192 not $191) and P2P users (the total should be $268 not $267), though perhaps this is due to rounding errors from the original data. More important, however, is a bigger math error in the chart as NPD Group significantly understates the difference between P2P and non-P2P users. In arriving at the grand total, it adds all the categories (physical CDs, paid downloads, subscription fees, merchandise, and concert tickets) plus the sub-total. In other words, it double counts the physical CDs, paid downloads, and subscription fees. The actual grand total of the five categories of spending is $206 per year for P2P users and only $138 for non-P2P users for a difference of 49.3 percent. There is obvious irony in NPD Group talking about the need for a licence to publish data only to get its math wrong, yet the real significance is that few would credibly argue that a nearly 50% increase in spending by P2P users can be simply chalked up to unsupported claims that P2P usage had no impact on consumer purchasing behaviour.
Read more in Music at Boing Boing
I write books. My latest is a YA science fiction novel called Homeland (it's the sequel to Little Brother). More books: Rapture of the Nerds (a novel, with Charlie Stross); With a Little Help (short stories); and The Great Big Beautiful Tomorrow (novella and nonfic). I speak all over the place and I tweet and tumble, too.