1992 CENSUS OF WHOLESALE TRADE COMMODITY LINE SALES =>CENSUS COVERAGE AND METHODOLOGY => STRUCTURE AND METHOD OF ENUMERATION All wholesale firms that had at least one quarter of payroll in 1992 were included in the census of wholesale trade and were mailed either a regular census form or a short form designed to collect basic data and classification information only. The coverage and the method of obtaining census information from each follow: Large companies, i.e., all multiunit firms and all single unit firms above the payroll size cutoff established to separate large from small employers, and a 10-percent sample of the small employers were mailed the appropriate 1992 Census of Distributive Trades establishment report forms. Although the payroll cutoff varied by kind of business, small employers generally included firms with one to three employees and represented about 10 percent of total wholesale sales. For the large companies, a report of company organization is conducted periodically to identify firms which operated establishments at more than one location and to obtain information on payroll and mid-March employment at each location. The 1991 Report of Company Organization was used as a coverage check in the census. In the 1992 Census, all multiestablishment firms were asked to notify the Census Bureau of any establishments for which a form was not received. Report forms were subsequently provided to the firms for these establishments. Small companies other than those included in the 10-percent sample described above were mailed the short forms, which did not include questions on sales by commodity lines and employment by principal activity. => METHOD OF CLASSIFYING KINDS OF BUSINESS Establishments receiving the regular census forms were classified on the basis of their answers to questions on sales by commodity lines and other inquiries. Those that received short forms were classified on the basis of their self designation and answers to other inquiries. =>COMPARABILITY OF THE 1987 AND 1992 CENSUSES The 1987 and 1992 censuses were conducted under similar conditions and procedures except for the following: => CLASSIFICATIONS In both 1992 and 1987, classifications are based on the 1987 Standard Industrial Classification (SIC) Manual (Standard Industrial Classification: 1987. For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402. Stock No. 041-001-00314-2). As a result of a later clarification in 1992, the sale of industrial controls has been classified in electrical apparatus and equipment, wiring supplies, and construction materials (SIC 5063) as it was in 1982 and all previous censuses. In 1987, the sale of industrial controls was classified in industrial machinery and equipment (SIC 5084). => GEOGRAPHIC AREAS The boundaries of a number of areas for which data are shown in the 1992 census are not the same as in the 1987 census because of annexations; other boundary changes; and redefinitions of metropolitan statistical areas (MSA's), primary metropolitan statistical areas (PMSA's), and consolidated metropolitan statistical areas (CMSA's) (Newly defined metropolitan areas (MA's) were announced by the Office of Management and Budget (OMB) effective June 30, 1993). =>COMMODITY LINE SALES => COMMODITY LINE INQUIRY COMPOSITION The commodity line inquiries on wholesale trade questionnaires were tailored to the kinds of business that would receive them. A broad commodity line was listed on a particular report form only if it accounted for a significant share of sales reported by the kind-of-business categories receiving that form in 1987. Because a complete set of broad lines was not present on any particular wholesale trade questionnaire, respondents sometimes found that part of their sales did not fit any available commodity line category. When this occurred, they were asked to report these sales on lines for "miscellaneous commodities - specify" and to describe the kinds of commodity represented. Census personnel subsequently attempted to classify each commodity based on the respondent's description and to assign the sales to the appropriate commodity line category. A small percentage of sales could not be classified and is therefore summarized in this report in a category called "miscellaneous commodities" (CL code 9800). The effect of excluding insignificant broad commodity lines on particular report forms is an understatement of the number of establishments handling each commodity line and the corresponding sales figure. The magnitude of this understatement for all commodity lines combined is indicated by the data presented for the "miscellaneous commodity" category. The effect will be greatest for commodity line categories that are minor components of total sales for a particular kind-of-business classification. => LIMITATIONS IN REPORTING SALES BY COMMODITY LINES There was a tendency on the part of respondents to fail to identify minor lines for their particular business and to include the sales of such minor lines with major ones. This deficiency has the effect of understating the number of outlets for individual commodity lines and affects the measurement of the volume of sales of individual lines. Commodity line categories by which individual wholesalers group their sales are not uniform and will not always correspond to categories established in a reporting system designed for general use. Because some wholesalers had little, if any, recorded information on sales by line of commodity, a substantial amount of estimation may be involved in the reporting of commodity lines. There is no assurance that the pattern for the establishments reporting sales by commodity lines is representative of those which did not report. It was concluded the effect of individual differences and of the use of approximations would be negligible in summary tabulations. Figures for commodity line sales should constitute useful approximations to serv many important current requirements and should be helpful in measuring important changes occurring over fairly long intervals, such as between successive censuses. => TREATMENT OF NONRESPONSE The reporting of commodity lines was incomplete or inadequate for establishments representing about 20 percent of the total dollar volume of sales. However, commodity line data have been expanded on the premise that the experience of those establishments not reporting commodity line data paralleled those establishments in the same kinds of business which reported this information. Due to the method by which commodity line sales are expanded, some inconsistencies between establishments for various lines may result. However, each estimate should be regarded as valid. Expansion methodology for 1987 and 1992 are essentially identical. In both cases, commodity line data were expanded at the lowest published level of geography and kind-of-business classification based on reporting experience at that level. If there were no reported commodity line data for a particular combination of kind of business and type of operation, expansion factors developed at the United States level were used to produce an estimate. The estimates from the most detailed kind of business and type of operation were then summed to produce higher level estimates, i.e., for broader kind-of-business and type-of-operation categories. => COVERAGE Coverage for each kind of business and type of operation shown indicate the degree to which establishments acceptably reported sales for broad commodity lines. Coverage was determined by dividing total sales of establishments reporting acceptable data for broad lines (whether or not additional detail lines were reported) by total sales of all establishments classified in that particular kind of business. Except when precluded by the census disclosure rules (see introduction), data have been shown for individual kinds of business when the dollar volume of reporting coverage accounted for 60 percent or more of sales after weighing commodity line sales of the sample of "small companies" as described in the "Census Coverage and Methodology" section above. The fact an establishment reported its sales by broad commodity line does not always mean all lines handled by the establishment were reported separately. => MEASURES OF SAMPLING VARIABILITY Because the commodity lines estimates are based in part on a sample, exact agreement with the results that would be obtained from a complete census of establishments using the same enumeration procedure should not be expected. However, because each establishment's chance of being selected for the sample was known, it was possible to estimate the sampling variability of the estimates made from the sample. The standard error of the estimate is a measure of the variability among the estimates from all possible samples of the same size and design and, thus, is a measure of the precision with which an estimate from a particular sample approximates the results of a complete enumeration. The coefficient of variation (expressed as a percent) is the standard error of the estimate divided by the value being estimated. Note that measures of sampling variability, such as the standard error or coefficient of variation, are estimated from the sample and are also subject to sampling variability. Tables of coefficients of variation for the broad and detail line estimates are shown in appendix H, tables 1 and 2. (Data were not available at time of publication. Please call 1-800-541-8345 or 301-457-2725 for a copy of this appendix) The coefficients of variation presented in these tables allow certain confidence statements about the sample estimates. The particular sample used in this survey was one of a large number of samples of the same size that could have been selected using the same design. In about 2 out of 3 (67 percent) of these samples, the estimates would differ from a complete enumeration by less than the corresponding percentages for that estimate shown in the coefficients of variation tables. In about 9 out of 10 (90 percent) of these samples, the estimates would differ from the results of a complete enumeration by less than 1.65 times the percentages shown. In about 19 out of 20 (95 percent) of the samples, the estimates would differ from the results of a complete enumeration by less than two times the percentage shown. To illustrate the computations involved in the above confidence statements as related to the dollar value estimates, assume that an estimate of sales is $10,750 million for a particular broad line, and the coefficient of variation for this estimate is 1.8 percent or 0.018. First, obtain the standard error of the estimate by multiplying the estimate by the coefficient of variation. In this example, $10,750 million times 0.018 yields a standard error of $194 million. The upper bound of the 67-percent confidence interval can then be formed by adding the standard error to the estimate and the lower bound formed by subtracting the standard error from the estimate. Thus, the 67-percent confidence interval for this example is $10,556 million to $10,944 million ($10,750 million plus or minus $194 million). If corresponding confidence intervals were constructed for all possible samples of the same size and design, approximately 2 out of 3 (67 percent) of the intervals would contain the figure obtained from a complete enumeration. Typical practice is to construct a 90- or 95-percent confidence interval. Using the same illustration as above, a 90-percent confidence interval would be $10,430 million to $11,070 million ($10,750 million plus or minus $320 million). Similarly, a 95-percent confidence interval is $10,362 million to $11,138 million ($10,750 million plus or minus $388 million). => DESCRIPTION OF THE FILES File 1, (WC92L1.dbf) presents data for all types of operations; merchant wholesalers, manufacturers' sales branches and offices; and agents, brokers, and commission merchants, respectively. It provides, for each kind of business and commodity line, the number of establishments handling the line and their sales of the line; the percentage of total sales of the specific kind of business accounted for by each of the lines carried; and the degree of specialization for each line in that line. Specialization is derived by computing sales of a line as a percentage of total sales of establishments that handled that particular line. Information on detailed commodity lines appear only in connection with specific kind of business to which the lines apply. Data relating to the detailed lines are indented below the applicable broad line in the tabulations. Commodity lines which present less than 0.05 percent of sales in a specific kind of business, and commodity lines which were not shown separately to avoid disclosure have been combined into a "all other commodities" category. Because of rounding procedures used, detail may not add to the totals. File 2, (WC92L2.dbf) provides summary data by broad commodity lines, including counts of establishments handling the line and total sales of the line. Also provided, within each broad commodity line, are counts of establishments carrying the line and the amount and percent of the line sold by various kinds of wholesalers. Available in both files is information on sales coverage of establishments reporting commodity lines that can be used as a guide in evaluating the validity of the commodity line data.