List_of_Billboard_200_number-one_albums_of_1981
The Billboard 200, published in Billboard magazine, is a weekly chart that ranks the 200 highest-selling music albums and EPs in the United States. Before Nielsen SoundScan began tracking sales in 1991, Billboard estimated the sales for the album charts from a representative sampling of record stores nationwide, which was gathered by telephone, fax or messenger service.[1] The data was based on reports from record stores, who ranked the popularity of the best-selling records but did not provide an actual sales figures.[2][3]