NPD receives data representing about two-thirds of U.S. retail sales and makes projections for the remainder of the market based on a sampling of consumers.
The figures do not include Canadian sales or those to "mom and pop" retailers, and are among the numerous data points used by analysts to measure the health of the video game market.
"Our numbers in terms of what we have shipped is definitely well above that [NPD] number. What NPD does not account for is the product that is in transit," said Nintendo spokeswoman Perrin Kaplan, who added that the company had a "robust" year.
