Thanks to yesterday's Shelf Awareness, I've got a better understanding of what's going on with the differences between the "bookstore sales" that PW Daily posts every month and the "book sales" that the Association of American Publishers cites. You'll recall that the bookstore revenue for 2007 was $16.77 billion, a 1.1 percent increase over the previous year's tally, a gain that was brought about by rallying sales in the late summer and fall, inspired by a book about a sullen teenager and his dead gay mentor fighting an undead wizard for control of a private school in England. Shelf Awareness explains that these figures, compiled by the Census Bureau, only include the sales of new books in brick-and-mortar outlets, with no "electronic home shopping, mail-order, or direct sale" venues considered.

When the AAP announces "book sales," by contrast, what they're really counting are the sales reported by 81 publishers, which probably corresponds to their membership list, if you want to take the time to count 'em. And, to recap last year's numbers, those publishers reported a total of $10.8 billion in sales, up 7.4 percent over 2006.

Of course, the first thing you'll notice is that there's a $6 billion gap between what the AAP members report and what the government says stores are selling—now that's an interesting story. How do we account for it? Do bookstore revenues include magazines, CDs, DVDs, and assorted knick-knacks? How much money are the smaller presses earning on the far end of the long tail? If you know, by all means, share.