Stratification

The primary stratification of the sampling frame is by industry group based on the

detail required for publication. We further stratify the sampling units within

industry group by a measure of size (substratify) related to their annual sales.

Sampling units expected to have a large effect on the precision of the estimates

are selected "with certainty." This means they are sure to be selected and will

represent only themselves (i.e., have a selection probability of 1 and a sampling

weight of 1). Within each industry stratum, we determine a substratum boundary

(or cutoff) that divides the certainty units from the noncertainty units. We base

these cutoffs on a statistical analysis of data from the 2012 Economic Census.

Accordingly, these values are on a 2012 sales basis. We also used this analysis

to determine the number of size substrata for each industry stratum and to set

preliminary sampling rates needed to achieve specified sampling variability

constraints on sales estimates for different industry groups. The size substrata

and sampling rates are later updated through analysis of the sampling frame.

Sample Selection

The first step in the sample selection identified firms selected with certainty. If a

firm's annual sales or end-of-year inventories are greater than the corresponding

certainty cutoff, we select that firm into the MWTS sample with certainty.

All firms not selected with certainty we subject to sampling. To be eligible for the initial 

sampling, a firm had to have nonzero payroll in 2014. We stratify the firms according to 

their major industry and their estimated sales (on a 2012 basis). Within each 

noncertainty stratum, we select a simple random sample of firms without replacement.

We conduct this process separately for each wholesale type of operation. The selected 

noncertainty firms were divided into two

approximately equal groups. For merchant wholesalers excluding Manufacturers

Sales Branches and Offices, one group is canvassed for both the monthly and

the annual survey, the other group is canvassed for only the annual survey. The

Manufacturers Sales Branch or Office and Agents and Brokers samples are only

canvassed in the annual survey. However, firms selected into the Manufacturers

Sales Branch or Office or Agent and Broker sample are included in the Monthly

Wholesale Trade Survey sample if that firm had activity inscope to the Monthly 

Wholesale Trade Survey.

Sample Maintenance

We update the sample on a quarterly basis to represent EINs issued since the initial sample 

selection. These new EINs, called births, are EINs recently assigned by the Internal Revenue 

Service (IRS) that have an active payroll filing requirement on the IRS Business Master File 

(BMF). An active payroll filing requirement indicates that the EIN is required to file payroll for the 
next quarterly period. The Social Security Administration attempts to assign industry 

classification to each new EIN.

EINs with an active payroll filing requirement on the IRS BMF are said to be "BMF active" and 

EINs with an inactive payroll filing requirement are said to be "BMF inactive."

We sample EIN births on a quarterly basis using a two-phase selection procedure. To be 

eligible for selection, a birth must either have no industry classification or be classified in an 

industry within the scope of the Service Annual Survey (SAS), the Annual Wholesale Trade 

Survey (AWTS), or the Annual Retail Trade Survey (ARTS), and it must meet certain criteria 

regarding its quarterly payroll. In the first phase, we stratify births by broad industry groups and 

a measure of size based on quarterly payroll. A relatively large sample is drawn and canvassed 

to obtain a more reliable measure of size, consisting of revenue in two recent months and a new 

or more detailed industry classification code. We contact births by telephone if they have not 

returned their questionnaire within 30 days.

Using this more reliable information, in the second phase we subject the selected births from the 

first phase to probability proportional-to-size sampling with overall probabilities equivalent to 

those used in drawing the initial AWTS sample from the December 2015 Business Register. 

Because of the time it takes for a new employer firm to acquire an EIN from the IRS and 

because of the time needed to accomplish the two-phase birth-selection procedure, we add 

births to the sample approximately nine months after they begin operation.

If a firm was selected with certainty and had more than one establishment at the time of 

sampling, any new establishments that the firm acquires, even if under new or different EINs, 

are included in the sample with certainty.

However, if a firm was selected with certainty and had only one establishment at the time of 

sampling, only future establishments associated with that firm’s originally-selected EIN are 

included in the sample with certainty; any new EINs that might later be associated with that firm 

are subjected to sampling through the quarterly birth-selection procedure.

To be eligible for the sample canvass and tabulation, a single establishment EIN, or at least one 

EIN associated with a firm selected in the noncertainty sampling operations must meet both of 

the following requirements: 

· It must be on the active payroll filing requirement on the IRS BMF.

· It must have been selected from the Business Register in either the initial sampling or during 

the quarterly birth-selection procedure.

We include any new establishments that a firm acquires, even if under new or different EINs, 

into the sample with the same sampling status as the original firm i.e., with the same initial 

sampling weight. For noncertainty firms, additional evaluation may be done in some instances to 

determine the feasibility of adding the new establishments by evaluating the effect of the new 

establishments on the industry estimates.

Similarly each quarter, we check against the current Business Register to determine if any EINs 

on the survey have become BMF inactive. Typically, we do not canvass BMF inactive EINs 

during the reference month. Likewise, if any EIN on the survey was BMF inactive in a previous 
reference month, or was part of an inactive sampling unit in the survey, and is now BMF active 

on the current Business Register, we again include these EINs in the canvass. In both cases, 

we only tabulate data for that portion of the reference month that these EINs reported payroll to 

the IRS.