Reference has also been made to results of other surveys, e.g. retail sales figures. Approximately 800 renter households are enumerated monthly. Telephone interviews and central data extraction from administrative records are also means of price collection. For heterogeneous items, average of price relatives is calculated. A standard Laspeyres formula is used.
Period covered by expenditure weights corresponds to the base price period.
Information on the portion of price change due to quality difference is obtained from the retail outlets wherever possible. Where such information cannot be obtained, quality adjustment is achieved through splicing. Field supervisors sample check and verify the price quotations collected by enumerators, and pay supervisory visits to ensure that the practices in data collection are correct. Price quotations and item indices with significant movements are flagged by the computer system for manual checking. Aggregate series are derived from lower level seasonally adjusted series.