Implementing the New Sample Design for the Current Employment Statistics Survey

Business Economics, Oct, 2000 by Patricia M. Getz

After the full implementation of the sample redesign is completed in 2003, BLS plans to begin a regular program of ongoing sample rotation, primarily to reduce respondent burden and related sample attrition. The largest units in the sample (tentatively defined as those with employment of 1000 or more) will not be rotated. The exact rotation period, or length of time a unit is in the sample, will be determined based on solicitation and data collection cost constraints.

Estimation formulas

In order to support the new sample design, improved estimators also have been developed and tested for the CES survey. The primary difference from the current CES estimator is the application of a weight to each sample unit in the estimation process. The weights are derived from population sampling fractions and are a standard feature of probability sample estimators. A sampled unit's weight is the inverse of its probability of selection; for example, a sample unit selected from a cell where one in ten units are selected will have a weight of ten, because it represents itself and nine other units. Previously, CES used an unweighted ratio estimator, known as the link relative, for the all-employee estimates. The new estimator is defined as a weighted link relative. There will be no level shifts or series breaks in the all-employee series, because the redesign estimates, like the historical published series, are anchored once a year to the benchmark level derived from the UI universe count of employment.

In order to prevent series breaks in the hours and earnings estimates, the initial implementation of the redesign also utilizes the weighted link relative estimator for these data types; and the first month's redesign estimate links to the final month's estimate produced under the old sample design. By utilizing the weighted link relative methodology for hours and earnings, the new sample design can be incorporated without subjecting these series to level shifts. BLS will implement any necessary level shifts in 2003, the final year of redesign implementation. In addition to introducing the final set of industries under a probability sample, 2003 also will feature the conversion from an SIC to a NAICS industry coding structure. Thus any series breaks, or level shifts, needed in the CES hours and earnings series from either the redesign or the coding structure changes will be incorporated simultaneously.

Business birth and death estimation

Regular updating of the CES sample frame with information from the UI universe files will help keep the CES survey current with respect to employment from business births and business deaths. The most timely UI universe files available, however, always will be a minimum of nine months out-of-date. The CES survey thus cannot rely on regular frame maintenance alone to provide estimates for business birth and death employment contributions. BLS has researched both sample-based and model-based approaches to measuring birth units that have not yet appeared on the UI universe frame. The research demonstrated that sampling for births was not feasible in the very short CES production timeframes. BLS is therefore utilizing a model-based approach for this component.