relatively small expenditure items for 2 consecutive weeks. A sample of 8,020 addresses are contacted each year to participate in the Diary Survey, so the effective annual sample size participating in this survey is 5,870 households, spaced across the 52 weeks in the year. The CEX has many uses in the governmental statistical framework. Its primary use in the CPI computation is to construct the quantities qhz0 which underlie the CPI computation. It has also been used “to select new market baskets of goods and services for the index, to determine the relative importance of components, and to derive new cost weights for the baskets” (U.S. Department of Labor, 2000).

Point of Purchase Survey and Commodities and Services Survey

The goal of the Point of Purchase Survey (POPS) is to determine the prices to be used in the CPI computation. The first stage of this survey is a national probability sample of household units, conducted by the Census Bureau, whose primary aim is to define the outlets to be sampled to obtain price data. The survey began in 1978 as a personal interview (and was referred to as CPOPS, for Continuing Point of Purchase Survey). In 1999 BLS revised this survey as a telephone interview, referred to as TPOPS (for Telephone Point of Purchase Survey). CPOPS was conducted annually over a period of 4 to 6 weeks, usually beginning in April; TPOPS interviews households every quarter. In CPOPS approximately one-fifth of the PSUs were sampled each year; the goal in TPOPS is to increase this sampling rate so that one-fourth of the PSUs are sampled each year. All consumer units in the selected household are asked to recall whether or not they purchased categories of goods and services within a specified recall period (varying from 1 week to 5 years, depending on the purchase cycle of the category) and, if so, the expenditure amounts and the names and locations of all places of purchase. Based on the responses to this survey of household units, a frame of outlets is defined for outlet selection. Since approximately one-fourth of the PSUs are currently sampled each year, after the survey of household units the frame of outlets determined by the survey is unchanged for 4 years.

The commodities and services are grouped into POPS categories, consisting of combinations of some of the ELIs; there were 174 POPS categories in 1997 (Bureau of Labor Statistics, 1997a). For example, POPS category 127, materials and supplies for major home repairs, consists of two of the ELIs of item stratum 2401, ELIs 24013 and 24014. POPS category 129, hardware items, hand tools, and other materials for minor home repairs, contains the other four ELIs of item stratum 2401—24011, 24012, 24015, and 24016; it also contains ELI 24041, miscellaneous supplies and equipment; ELI 32043, other hardware; and ELI 32044, nonpowered hand tools.

For the purpose of outlet selection, the BLS has aggregated the POPS categories into eight categories and the PSUs into ten groups (see Bureau of Labor Statistics, 1997a:). After a PSU group has been surveyed, the ELIs to be priced



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