CES Birth/Death Model Frequently Asked Questions

Q: Do the birth/death factors vary from first preliminary to final estimate?

A: The birth/death factor for a given month does not change between 1st preliminary, 2nd preliminary, and final sample-based estimates.

Q: Are birth/death factors seasonally adjusted?

A: No, they are calculated using population data that is not seasonally adjusted and the factors are applied to the sample-based not seasonally adjusted estimates.  Months with generally strong seasonal increases such as April, May and June generally have a relatively large positive factor.  Conversely, months with overall strong seasonal decreases, such as January, generally have a relatively large negative factor.

Q: Can I subtract the birth/death adjustment from the seasonally adjusted over-the-month change to determine what it is adding to employment?

A: No.  Birth/death factors are a component of the not seasonally adjusted estimate and therefore are not directly comparable to the seasonally adjusted monthly changes.  Instead, the birth/death factor should be assessed in the context of its effect on the not seasonally adjusted estimate.

Q: Can BLS provide an estimate of the contribution of the birth/death adjustment to the seasonally adjusted monthly payroll change? 

A: BLS does not calculate an estimate of the seasonally adjusted contribution of the birth/death model.  The sample, the imputation of business births using deaths, and the net birth/death model are all necessary components for obtaining an accurate total employment estimate.  The components are not seasonally adjusted separately because they do not have any particular economic meaning in and of themselves.

Q: How frequently are the birth/death figures revised and why do the values change?

A: Birth/death numbers are revised once a year with the benchmark revision.  There are two reasons that the birth/death values change with the update.  First, each year another 12 months of data are added to the historical series used in fitting the models.  As a result of the additional data, the models provide updated results.  Secondly, in general the amount of birth/death required is of a larger magnitude the further the reference month is from the benchmark.  As a result one model is used to provide birth/death values for the first 12 reference months after the benchmark month, and the second model is used for providing birth/death values for 13 to 21 months from the benchmark.  As an example, the first preliminary estimate for June 2003 was produced on the March 2002 Benchmark using a second year model.  When the March 2003 Benchmark was implemented, the June 2003 birth/death factor came from a first year model.

Q: How long has CES been using the birth/death factors and is the history of birth/death available?

A: Implementation of the birth/death factors was associated with the implementation of a new probability-based sample design and estimator.  The new methodology was phased in gradually under the following schedule:  Beginning in June 2000 (with March 1999 Benchmark), Wholesale Trade on an SIC-basis was under the new methodology; in June 2001 (with the March 2000 Benchmark), Mining, Construction, and Manufacturing, on an SIC-basis, were added; in June 2002 (with the March 2001 Benchmark), all of Total Private with the exception of Services were under the new methodology; with the conversion to NAICS in June 2003 (with the March 2002 Benchmark), all of the Total Private industries were produced under the new methodology.

Historical Birth/Death factors are available at www.bls.gov/ces/cesbdhst.htm.

Q: Were estimates purely sample based before 2003?

A: No, prior to the implementation of birth/death modeling, CES used a technique known as bias adjustment to account for business births, business deaths, and other limitations of the survey.

Return to CES Net Birth/Death Model.


Last Modified Date: May 6, 2008