1

With the release of January 2003 data from the Current

Population Survey (CPS), the Bureau of Labor

Statistics (BLS) incorporated several major

changes and revisions to the time series from the survey.1

These included two adjustments to CPS population controls

that created “bumps” in the historical series of CPS data—

one between December 1999 and January 2000, and another

between December 2002 and January 2003. BLS recognizes

the preference of some data users to have an uninterrupted

time series for historical trend analysis. This article presents

what BLS believes to be a reasonable method to “smooth”

the bumps in the employment series of the major demographic

groups for which it publishes monthly data.

The revisions to CPS data

Of the two population control adjustments, the largest—

between December 1999 and January 2000—reflected the

switch to population controls based on data from the 2000

decennial census as enumerated. Updates based on the latest

decennial census information are generally done 3 or 4 years

following each census, and, after the last two censuses, BLS

has revised CPS time series data back to the census reference

year. BLS revised CPS data from January 2000 to December

2002 to incorporate higher population estimates from the

census, as well as new, higher estimates of population growth

since the census. At the start of the revision period (January

2000), the new controls raised the civilian noninstitutional

population (CNP) aged 16 and older by about 2.6 million. By

December 2002, the CNP was 3.8 million greater than originally

estimated.

In addition to population data from the decennial census,

BLS also receives intercensal population data annually from

the U.S. Census Bureau. These annual population updates

are based on recent data on net births and deaths,

immigration, and emigration, as well as changes in the

methodology that the Census Bureau uses to project the

population. These updated estimates are usually incorporated

Creating Comparability in CPS

Employment Series

into the January data. Sometimes these intercensal updates

are sizeable, as was the case in January 2003. The Census

Bureau estimated that the CNP had registered an additional

increase of 941,000 from early 2000 to December 2002. Because

this information was not available in time for incorporation

into the already planned revision of January 2000 to December

2002 data (based on Census 2000 data), the entire adjustment

(+941,000) was added to the population in January 2003.

Given the amount of effort needed to completely revise and

verify time series for all employment and unemployment

estimates produced from the CPS and given that the revisions

would be negligible for most series, BLS does not revise

historical data to reflect these annual population adjustments.

Smoothing the series

As mentioned above, the two updates to the population

controls used in the CPS introduced in January 2003 created

two breaks in the historical data series. For many of the CPS

data series, the new population controls had little significant

effect. However, the adjustments did cause a notable rise in

some series, such as employment. Several data users have

requested that BLS suggest a method to create a smoothed

employment series back to 1990 for the major demographic

groups for which it publishes monthly data. Research was

done and the technique chosen to smooth the bumps in the

data series was to calculate the difference between the new

and old estimates at the point of the break and to wedge that

difference back into the series over the period during which

it is assumed to have accumulated.

Two charts showing the effects of using this smoothing

technique on the total employment and total unemployment

series (seasonally adjusted) are presented on the following

page. Clearly, the smoothing technique had a notable effect

on the employment series, but it had almost no effect on the

unemployment series. As is shown in the first chart, the

smoothing technique eliminated the bumps in employment

in January 2000 and January 2003, while preserving the shape

of the original trend line. A limitation of this technique is that

it assumes that the population growth was distributed evenly

over the adjustment period, which may not be the case.

The method

Two adjustment factors must be derived in order to correct

for the two breaks that occurred in the data series in January

2000 and January 2003. Both adjustment factors are calculated

the same way, as shown in the equation:

1 For discussion of the changes and revisions and the effect that they

had on the CPS data, see “Revisions to the Current Population Survey

Effective in January 2003” in the February 2003 issue of Employment

& Earnings available on the Internet at http://www.bls.gov/cps/

rvcpso3.pdf.

Marisa L. Di Natale

Marisa L. Di Natale is an economist in the Division of Labor Force

Statistics, Office of Employment and Unemployment Statistics,

Bureau of Labor Statistics. Telephone: (202) 691-6378; e-mail:

Dinatale.Marisa@bls.gov.
2

Adjustment factor = (new estimate at break point/

old estimate at break point) - 1

The method for calculating the adjustment factors for total

employment is illustrated below.

1. The not seasonally adjusted employment level in

January 2000 after the Census 2000-based revision

was 134,912,000. This was divided by the not

seasonally adjusted employment level in January

2000 as originally published (before the revision),

which was 133,357,000.

Total civilian employment, seasonally adjusted

110,000

115,000

120,000

125,000

130,000

135,000

140,000

Jan-90Jan-91Jan-92Jan-93Jan-94Jan-95Jan-96Jan-97Jan-98Jan-99Jan-00Jan-01Jan-02Jan-03

Employment level (thousands)

Official series Smoothed series 

Total unemployment, seasonally adjusted

4,000

5,000

6,000

7,000

8,000

9,000

10,000

11,000

Jan-90Jan-91Jan-92Jan-93Jan-94Jan-95Jan-96Jan-97Jan-98Jan-99Jan-00Jan-01Jan-02Jan-03

Unemployment level (thousands)

Official series Smoothed series

134,912,000/133,357,000= 1.011660 - 1 = 0.011660

2. To calculate the second adjustment factor, the

revised, not seasonally adjusted December 2002

employment level of 137,735,000 was divided by the

unrevised, not seasonally adjusted employment

level for that month, 137,159,000.2

137,735,000/137,159,000 = 1.004200 - 1 = 0.004200

2 These December 2002 estimates are not seasonally adjusted,

noncomposited estimates, and do not appear in official BLS data

series. They were published in “Revisions to the Current Population

Survey Effective in January 2003,” previously cited.
3

These adjustment factors represent the increase in

employment that must be distributed over the period for which

estimates are to be revised. So, the first factor should be

applied to the 120 months from January 1990 through

December 1999, and the second factor should be applied to

the 35 months from January 2000 through November 2002.

The following equation represents the calculation that

must be done for each month in order to derive a “smoothed”

estimate, where EMsmoothed equals this estimate and EM equals

the estimate in the Mth month from 1 to 120 for the first

factor, and from 1 to 35 for the second factor, for which the

formula is being applied.

EMsmoothed = EM ((1 + (factor/120 x M))

For example, the seasonally adjusted employment level in

January 1990 was 119,081,000. Take the adjustment factor

for total employment, which is 0.011660, and plug this into

the formula above.

EMsmoothed =119,081,000 ((1 + (0.011660/120) x 1))

= 119,093,000

This revised employment level applies the Census 2000-

based population controls to the employment level in January

1990. The formula for February 1990 would look like this:

EMsmoothed =119,059,000 ((1 + (0.011660/120) x 2))

= 119,082,000

Employment Factor 1 Factor 2

series (Jan. 1990- (Jan. 2000-

Dec. 1999) Nov. 2002)

Total, 16 years and over 0.011660 0.004200

Men, 20 years and older 0.013534 0.004603

Women, 20 years and

older 0.011757 0.004126

Both sexes, 16 to 19 years -0.008036 0.000164

White 0.004066 0.003762

Black or African American 0.016231 -0.000133

Hispanic or Latino

ethnicity 0.084389 0.019715

The adjustment factors for employment for each of the

major demographic groups are presented in the table below.

Factor 1 refers to the factor to be applied to data for January

1990 through December 1999. This factor adjusts the series

for the revisions due to the population increase from the

decennial census data. Factor 2 refers to the growth in the

population that was incorporated in the January 2003 data

(+941,000) and should be applied to data for each month

between January 2000 and November 2002.