The Johnson Redbook Index is a sales-weighted of year-over-year same-store sales growth in a sample of large US general merchandise retailers representing about 9,000 stores. Same-store sales are sales in stores continuously open for 12 months or longer. By dollar value, the Index represents over 80% of the equivalent 'official' retail sales series collected and published by the US Department of Commerce. Redbook compiles the Index by collecting and interpreting performance estimates from retailers. The Index and its sub-groups are sales-weighted aggregates of these estimates. Weeks are retail weeks (Sunday to Saturday), and equally weighted within the month.