Bureau of Labor Statistics 

Current Population Survey (CPS) 

Technical Documentation 

April 2014

Redesign of the Sample for the 

Current Population Survey

 In accordance with usual practice, the sample for the Current Population Survey (CPS) has 

been redesigned based on information from Census 2010. The sample redesign is expected to 

have a negligible effect on published estimates. 

 The CPS—also known as the household survey—is a monthly survey of households that 

provides information on the labor force status, demographics, and other characteristics of the 

nation's civilian noninstitutional population age 16 and over. Historically, the CPS sample has 

been redesigned after each decennial census. The last sample redesign occurred in 2004 and 

introduced a sample based on Census 2000. 

 The introduction of the new CPS sample began in April 2014 and will be completed in July 

2015. Households in the new sample will be phased into the survey by using the normal 

“rotation” group pattern in the survey’s design, with one rotation group per month. Households 

interviewed in the survey are divided into eight approximately equal panels, called rotation 

groups. A rotation group is interviewed for 4 consecutive months, temporarily leaves the sample 

for 8 months, and then returns for 4 more consecutive months before retiring permanently from 

the CPS (after a total of eight interviews). Each month, one-eighth of the sample is being 

interviewed for the first time, one-eighth for the second time, and so on. This rotation scheme 

has been in use since July 1953 and strengthens the reliability of estimates of month-to-month 

change as well as estimates of year-to-year change.

 The CPS is conducted in approximately 60,000 eligible housing units throughout the United 

States. (“Eligible” refers to an occupied housing unit having at least one person in the civilian 

noninstitutional population.) This sample includes 10,000 eligible housing units from the 

monthly supplementary sample to improve state-level estimates of health insurance coverage for 

low-income children, also known as the CHIP expansion. The supplementary sample has been 

part of the official CPS since July 2001. Thirty-two states plus the District of Columbia have 

this supplementary sample each month. 

 The CPS sample is a probability sample based on a stratified two-stage sampling scheme: 

selection of sample primary sampling units (PSUs) and selection of sample housing units within 

those PSUs. In general, the CPS sample is selected from lists of addresses obtained from the 

Master Address File with updates from the United States Postal Service twice a year. The 

Master Address File is the Census Bureau’s permanent list of addresses, including their 
2

geographic locations, for individual living quarters. It is continuously maintained through 

partnerships with the United States Postal Service; with Federal, State, regional, and local 

agencies; and with the private sector; and it is used as a sample frame by many Census Bureau 

demographic surveys. The CHIP sample selection methodology is similar to that used for the 

CPS. 

State-based design 

 In the first stage of sampling, PSUs are selected. These PSUs consist of counties or groups of 

contiguous counties in the United States, and are grouped into strata. The CPS is a state-based 

design. Therefore, all PSUs and strata are defined within state boundaries and the sample is 

allocated among the states to produce state and national estimates with the required reliability, 

while keeping total sample size to a minimum. The specified coefficient of variation (CV) 

requirement for the monthly unemployment level for the nation, given a 6 percent unemployment 

rate, is 1.9 percent or less. (The CV of an estimate is the estimate itself divided by its standard 

error, usually expressed as a percent.) This CV is based on the requirement that a difference of 

0.2 percentage points in the unemployment rate between 2 consecutive months be statistically 

significant at the 90 percent level of confidence. Additionally, the required CV on the annual 

average unemployment level for each state and the District of Columbia, given a 6 percent 

unemployment rate, is 8 percent or less. For New York and California, the state reliability 

requirement applies to the following substate areas: New York City (five boroughs only), the 

balance of New York State, Los Angeles County, and the balance of California. 

First stage of the sample design: PSU stratification and selection 

 The variables chosen for grouping PSUs in each state into strata reflect the primary interest of 

the CPS in maximizing the reliability of estimates of labor force characteristics. The same set of 

stratification variables from Census 2010 and the American Community Survey (ACS) are used 

for each state: unemployment statistics by gender; the number of families maintained by women; 

and the proportion of occupied housing units with three or more people. In addition, the number 

of persons employed in selected industries and the average monthly wage for selected industries 

are used as stratification variables in some states. The industry-specific data are averages over 

the period 2000 through 2008 and are obtained from the BLS Quarterly Census of Employment 

and Wages (QCEW) program. 

 Each stratum consists of one or more PSUs. Within each stratum, a single PSU is chosen for 

the sample, with probability proportional to its population as of the 2010 Census. Some strata 

have only one PSU, and each is included in the sample as a self-representing PSU; these strata 

generally include the most populous counties within each state. The remaining PSUs are 

grouped into non-self-representing strata within state boundaries. In each of these strata, one 

PSU is selected to represent all of the PSUs in that stratum. 

 

 The PSUs, strata, and sample PSUs are the same for CPS and CHIP. This differs from the 

2000 sample design, which had three states with different designs. In total, 852 PSUs (1,385 
3

counties) from a total of 1,987 PSUs (3,143 counties) in the United States are in sample for 

either just the basic CPS or for both the basic CPS and the CHIP expansion. 

Second stage of the sample design: selection of housing units 

 The 2010 sample design comprises three frames: unit, coverage improvement, and group 

quarters. The unit frame consists of housing units in census blocks that contain a very high 

proportion of complete addresses. It covers most of the population and accounts for 

approximately 95 percent of the CPS sample. It is updated every 6 months with new growth 

records and will be sampled from annually. The coverage improvement frame (in 13 targeted 

states) is intended to improve the coverage of the unit frame. The coverage improvement frame 

is updated annually with information from July Master Address File extracts. There is a single 

group quarters frame in the 2010 sample design and its sample is selected in a 3-year cycle. 

 Within these sampling frames, housing units are sorted based on characteristics from the 

American Community Survey and geography. Then, from each frame, a systematic sample of 

addresses within the sample PSUs is obtained. Most of the sample addresses are selected in a 

single stage of sampling within the selected PSUs; for a relatively small proportion, an additional 

stage of selection within the PSU is necessary. 

Major differences from the 2000 CPS sample design 

 The 2010 sample design differs from that of 2000 in a variety of ways. These changes have 

resulted after consideration of numerous factors, including improving reliability of the estimates, 

minimizing costs, and maximizing comparability of estimates across time. Major changes 

include the following. 

1) With the phase-in beginning in 2014, sample is now selected from the continually 

updated Master Address File, and American Community Survey (ACS) data is used 

to sort and stratify the housing units on the Master Address File. Previously, sample 

was selected from decennial census address lists and stratification was done using 

information also from the decennial census. 

2) In the past, the CPS sample universe was distributed across four frames: unit, permit, 

group quarters, and area, with approximately 80 percent of the CPS sample coming 

from the unit frame. As mentioned previously, the 2010 sample design comprises 

three frames: unit (updated with new growth records), coverage improvement, and 

group quarters. As the result of improved flexibility and reduced complexity of block 

listing via the coverage improvement frame, an area frame no longer exists. Instead, 

the block listing process will enable a flexible workload that can change as often as 

annually, depending on budget resources and on the need for coverage improvement. 

Rather than having group quarters split between the group quarters frame and the area 

frame as in past designs, there is a now a single group quarters frame. An additional 
4

change is the exclusion of military group quarters from the sampling universe since 

research showed that they are extremely unlikely to convert to civilian group quarters. 

 

3) In past designs, the CPS had selected a decade of sample housing units all at once, 

occurring just after the decennial census, with periodic supplementation of new 

construction through sampling of building permits and area listing results. The 

selected housing units were then parsed into monthly samples throughout the decade. 

This approach was the most cost effective and sensible method of sampling in the 

context of once-a-decade operations. 

 

In the 2010 sample design, sampling occurs annually for the unit frame. This changes 

the second-stage sample selection of housing units from once-a-decade sampling to 

annual sampling. The benefits of selecting a fully representative sample of housing 

units on an annual basis include: 

• Better control of survey sample size. 

• More accurate addresses due to twice-a-year updates of valid/invalid status, 

geocoding errors, and geography changes of previously existing records that 

are eligible for selection. 

• Ability to modify or select new samples more quickly in response to 

population shifts in order to meet reliability criteria. 

• More flexibility in accommodating sample expansions and contractions in 

response to changes in budget or data requirements. 

• Ability to implement methodological changes and process improvements 

more quickly and easily than before. 

• Potential to reduce variances on annual average estimates with annual 

sampling; this is a potential for cost saving because less sample is needed. 

Note that annual sampling does not apply to the group quarters frame, where sample 

is selected 3 years at a time, or to the first-stage sample selection of the PSUs. Also, 

a housing unit selected by any demographic survey will not be available for selection 

by subsequent surveys until 5 years after its last interview.