These data come from the annual retail sales survey and data on the annual retail turnover value of services. Major revision of weights every 5 to 10 years. Each year weights are updated by the relative price changes since the previous year. Retail outlets are selected according to the biggest share in retail turnover of particular products or services. Index for the group is weighted arithmetic average of the indices for the categories.
Total index is weighted arithmetic average of the indices for the groups.
Laspeyres formula is used to aggregate basic item indices to obtain category, group and the total indices. Annually, i.e. at the beginning of the calendar year. The CBS price statistics staff does the second verification. All verifications are done during the computation of the index.