Confidentiality: Title 13 of the United States Code authorizes the Census Bureau to conduct censuses and surveys. Section 9 of the same Title requires that any information collected from the public under the authority of Title 13 be maintained as confidential. Section 214 of Title 13 and Sections 3559 and 3571 of Title 18 of the United States Code provide for the imposition of penalties of up to five years in prison and up to $250,000 in fines for wrongful disclosure of confidential census information. The Census Bureau's internal Disclosure Review Board sets the confidentiality rules for all data releases. A checklist approach is used to ensure that all potential risks to the confidentiality of the data are considered and addressed.
Disclosure Statement: A disclosure of data occurs when an individual can use published statistical information to identify either an individual or firm that has provided information under a pledge of confidentiality. Disclosure limitation is the process used to protect the confidentiality of the survey data provided by an individual or firm. Using disclosure limitation procedures, the Census Bureau modifies or removes the characteristics that put confidential information at risk for disclosure. Although it may appear that a table shows information about a specific individual or business, the Census Bureau has taken steps to disguise or suppress the original data while making sure the results are still useful. The techniques used by the Census Bureau to protect confidentiality in tabulations vary, depending on the type of data.
Sampling Frame: Companies, parts of companies (defined by Employer Identification Numbers, or EINs), and single-unit establishments (also defined by EINs) that are located in the United States, have paid employees, and are classified as merchant wholesalers, excluding manufacturer's sales branches and offices. The EIN is the identifier employer businesses use to report Social Security payroll withholdings to the Federal government. Read more [PDF] about the MWTS Sampling Frame.
Sample Design and Size: The MWTS uses a stratified, one-stage design with primary strata defined by industry (e.g., Motor Vehicle and Motor Vehicle Parts, Furniture and Home Furnishings, Grocery, etc.). There are 42 primary strata. The primary strata are substratified into 4, 7, 10, or 13 annual sales size strata. The largest sales size stratum within each industry stratum consists of companies, all of which are selected with certainty (sampling weight equal to one). The other strata are populated by EINs. Sample sizes are computed to meet multiple coefficient of variation constraints on estimated annual sales and end-of-year inventory totals. Constraints are specified at detailed industry levels and at broad industry levels up to the total wholesale level. Sampling weights range from 1 to 500. Units are selected independently between strata using simple random sampling without replacement within the size substrata. The sample consists of approximately 1,200 certainty companies and 3,000 EINs. Updates to the sample are made on a quarterly basis to account for new businesses, deaths, and other changes to the universe. Read more [PDF] about how the MWTS sample is stratified, selected, and maintained.
Data Collection: Data are collected by mail, fax, internet, and telephone. Response is voluntary. Questionnaires are mailed each month and request data for the month just ending.
Data Items Requested: Data items requested include monthly sales, end-of-month inventories, number of establishments covered by the report, and the ending date of the report period if the data provided are for a period other than the calendar month.
Nonresponse: Data are imputed for unit nonresponse, item nonresponse, and for reported data that fail edits. Imputed data are based on responses from similar-sized units classified in the same industry. Read more [PDF] about how nonresponse is handled on the MWTS.
Estimation and Sampling Variance: Preliminary estimates are published approximately 40 days after the data month and are revised approximately 30 days later. Total estimates are equivalent to Horvitz-Thompson estimates, that is, they are computed by summing weighted data (reported or imputed) where the weight for a given unit is the reciprocal its probability of being selected into the sample. Variances are estimated using the method of random groups and are used to determine if measured changes are statistically significant. Read more [PDF] about how the MWTS arrives at its estimates and the reliabilty of using those estimates.
Benchmarking: Monthly estimates are benchmarked to annual survey estimates that have been adjusted using the latest available Economic Census results. Month-to-month change estimates are computed from the benchmarked total estimates.
Seasonal Adjustment: Estimates are adjusted for seasonal variation and trading-day differences using the Census Bureau's X-13 ARIMA-SEATS program using the X-11 filter-based adjustment procedure. Read more about how the MWTS uses seasonal adjustments to produce high quality statistics about our nation's economy.
Important Uses of Results: The Bureau of Economic Analysis (BEA) is the primary Federal user of data collected in the MWTS. BEA uses this information to prepare the national income and product accounts, input-output accounts, and gross domestic product.