1. Workshop on Price Index Compilation Issues February 23-27, 2015 Sample Design, Selection, and Maintenance Gefinor Rotana Hotel, Beirut, Lebanon

2. Sample Design and Selection Lecture outline Introduction Common problems in price survey sampling Where to start Sample design Sample selection and recruitment

3. Sample Design and Selection Introduction Use of statistically sound sampling techniques vs. judgmental samples Approach dependent on availability of data Need to maintain sample size

4. Sample Design and Selection Common Problems in Price Sampling Without probability sampling methods it is difficult to measure accuracy and optimize sample Attrition of sampled establishments and products at the same time as new goods appear Lack of up-to-date sampling frame Voluntary nature of most price surveys Purposive sampling increases chance of bias

5. Sample Design and Selection Where to Start Objectives of the surveys measure of inflation, use as deflator monthly or quarterly estimates level of detail for publication important commodities, groupings, industries

6. Sample Design and Selection Coverage National, regional, urban only, selected areas Economic activities (industry, services, etc.) Income / population groups (e.g., low, middle, high income households; family size; military)

7. Sample Design and Selection Data to be collected Purchaser, producer, basic price? Type of price (transaction, list, average, cost plus) Time of recording (cash or accrual) Detailed specification of the product which includes all the terms involved in the purchase Temporary non-availability of some prices Point in time price or average over the period

8. Sample Design and Selection Sampling frames Business register (complete and up-to- date?) Household lists Stratification variables included (ISIC, output or sales, location; income, household expenditures, etc.)

9. Sample Design and Selection Level of accuracy and sample size Probability sampling enables us to use population variance to determine sample size Non-probability sampling must be applied carefully to ensure adequate representation

10. Sample Design and Selection Available resources such as staff involved and method of collection are constraints Legislative issues such as voluntary or mandatory reporting and laws governing confidentiality or privacy affect our procedures

11. Sample Design and Selection Sample Design Probability vs. non-probability Simple random sampling Stratified random sampling Probability proportionate to size (PPS) Cutoff samples

12. Sample Design and Selection Sample frame selection business register, business census, industry surveys population census, housing lists, household surveys Sample structure and stratification PPI, XMPI—region, industry, establishment, product CPI—area, item, outlet, variety

13. Sample Design and Selection Sample allocation—what will resources allow? XMPI, PPI by product and industry; CPI by area and item specific products, industries, items that should be published cutoff sampling may be best approach

14. Sample Design and Selection Sample Selection and Recruitment Specific issues in the CPI sample design selection of geographic areas (cities and rural areas) selection of outlets and/or markets for pricing selection of items to include in the basket number of price observations per item frequency of price collection per item (often determined by price variability) selection of individual varieties to represent items

15. Sample Design and Selection Specific issues in the XMPI, PPI sample design selection of industrial coverage (mining, manufacturing, energy, agriculture, transport, etc.) selection of representative industries selection of representative establishments selection of representative products/commodities frequency of price collection per products selection of individual transactions to represent products

16. Sample Design and Selection Recruitment of establishments/outlets via personal visit Selecting transactions / varieties for pricing identify important price determining characteristics record the detailed specifications on collection document

17. Thank you