Last week was the first time that Nielsen BookScan added Wal-Mart data to its report on book sales. Wal-Mart sales are now part of BookScan’s mass merchandisers & other strata and as you might suspect, provided a huge boost to sales in that segment. In the week ended January 6, 2013, units in the segment rose 65% to over 1.8 million units from 1.1 million in the first week of January 2012.

The addition of Wal-Mart will complicate comparing weekly sales in 2013 to those in 2012. In the first week of 2013, the Wal-Mart sales helped to boost total units up 3% from the same week in 2012. Sales in the retail & club strata, which account for the majority of unit sales, fell 4% in the week ending January 6, 2013 compared to the week ended January 8, 2012.