Rankings reflect sales at almost 4,000 bookstores plus wholesalers serving 50,000 other retailers (gift shops, department stores, newsstands, supermarkets), statistically weighted to represent all such outlets nationwide.

The numbers are statistically weighted to represent sales in all such outlets nationwide.

The estimates are weighted to represent national estimates.

Rankings reflect sales figures, for the week ending May 10, at 3,985 bookstores plus wholesalers serving 60,000 other retailers, statistically weighted to represent sales in all such outlets nationwide.

All analyses were weighted to represent the total civilian, non-institutionalized United States population; they are, therefore, population prevalence estimates.

Rankings reflect sales, for the week ended June 4, at almost 4,000 bookstores plus wholesalers serving 50,000 other retailers, statistically weighted to represent all such outlets nationwide.

The universe of print book dealers is well established, and sales of print titles are statistically weighted to represent all outlets nationwide.

In many situations the sample fraction may be varied by stratum and data will have to be weighted to correctly represent the population.

Rankings reflect sales figures, for the week ending March 5, at 3,050 bookstores and wholesalers serving 28,000 other retailers (gift shops, department stores, newsstands, supermarkets), statistically weighted to represent sales in all such outlets nationwide.

Each month's survey is compared with a similar rental survey six months earlier, and the result is weighted to represent 30 percent of the entire Consumer Price Index.