Current Population Survey Design and Methodology - Census Bureau
Current Population Survey Design and Methodology - Census Bureau
Current Population Survey Design and Methodology - Census Bureau
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Chapter 3.<br />
<strong>Design</strong> of the <strong>Current</strong> <strong>Population</strong> <strong>Survey</strong> Sample<br />
INTRODUCTION<br />
For more than six decades, the <strong>Current</strong> <strong>Population</strong> <strong>Survey</strong><br />
(CPS) has been one of the major sources of up-to-date<br />
information on the labor force <strong>and</strong> demographic characteristics<br />
of the U.S. population. Because of the CPS’s importance<br />
<strong>and</strong> high profile, the reliability of the estimates has<br />
been evaluated periodically. The design has often been<br />
under close scrutiny in response to dem<strong>and</strong> for new data<br />
<strong>and</strong> to improve the reliability of the estimates by applying<br />
research findings <strong>and</strong> new types of information (especially<br />
census results). All changes are implemented with concern<br />
for minimizing cost <strong>and</strong> maximizing comparability of estimates<br />
across time. The methods used to select the sample<br />
households for the survey are evaluated after each decennial<br />
census. Based on these evaluations, the design of the<br />
survey is modified <strong>and</strong> systems are put in place to provide<br />
sample for the following decode. The most recent decennial<br />
revision incorporated new information from <strong>Census</strong><br />
2000 <strong>and</strong> was complete as of July 2005.<br />
This chapter describes the CPS sample design as of July<br />
2005. It is directed to a general audience <strong>and</strong> presents<br />
many topics with varying degrees of detail. The following<br />
section provides a broad overview of the CPS design <strong>and</strong><br />
is recommended for all readers. Later sections of this<br />
chapter provide a more in-depth description of the CPS<br />
design <strong>and</strong> are recommended for readers who require<br />
greater detail.<br />
SURVEY REQUIREMENTS AND DESIGN<br />
<strong>Survey</strong> Requirements<br />
The following list briefly describes the major characteristics<br />
of the CPS sample as of July 2005:<br />
1. The CPS sample is a probability sample.<br />
2. The sample is designed primarily to produce national<br />
<strong>and</strong> state estimates of labor force characteristics of<br />
the civilian noninstitutionalized population 16 years of<br />
age <strong>and</strong> older (CNP16+).<br />
3. The CPS sample consists of independent samples in<br />
each state <strong>and</strong> the District of Columbia. Each state<br />
sample is specifically tailored to the demographic <strong>and</strong><br />
labor market conditions that prevail in that particular<br />
state. California <strong>and</strong> New York State are further<br />
divided into two substate areas that also have independent<br />
designs: Los Angeles County <strong>and</strong> the rest of<br />
<strong>Current</strong> <strong>Population</strong> <strong>Survey</strong> TP66<br />
U.S. <strong>Bureau</strong> of Labor Statistics <strong>and</strong> U.S. <strong>Census</strong> <strong>Bureau</strong><br />
California; New York City <strong>and</strong> the rest of New York<br />
State. 1 Since the CPS design consists of independent<br />
designs for the states <strong>and</strong> substate areas, it is said to<br />
be state-based.<br />
4. Sample sizes are determined by reliability requirements<br />
that are expressed in terms of the coefficient of<br />
variation or CV. The CV is a relative measure of the<br />
sampling error <strong>and</strong> is calculated as sampling error<br />
divided by the expected value of the given characteristic.<br />
The specified CV requirement for the monthly<br />
unemployment level for the nation, given a 6 percent<br />
unemployment rate, is 1.9 percent. The 1.9 percent<br />
CV is based on the requirement that a difference of<br />
0.2 percentage points in the unemployment rate for<br />
two consecutive months be statistically significant at<br />
the 0.10 level.<br />
5. The required CV on the annual average unemployment<br />
level for each state, substate area, <strong>and</strong> the District of<br />
Columbia, given a 6 percent unemployment rate, is 8<br />
percent.<br />
Overview of <strong>Survey</strong> <strong>Design</strong><br />
The CPS sample is a multistage stratified sample of<br />
approximately 72,000 assigned housing units from 824<br />
sample areas designed to measure demographic <strong>and</strong> labor<br />
force characteristics of the civilian noninstitutionalized<br />
population 16 years of age <strong>and</strong> older. Approximately<br />
12,000 of the assigned housing units are sampled under<br />
the State Children’s Health Insurance Program (SCHIP)<br />
expansion that has been part of the official CPS sample<br />
since July 2001. The CPS samples housing units from lists<br />
of addresses obtained from the 2000 Decennial <strong>Census</strong> of<br />
<strong>Population</strong> <strong>and</strong> Housing. The sample is updated continuously<br />
for new housing built after <strong>Census</strong> 2000. The first<br />
stage of sampling involves dividing the United States into<br />
primary sampling units (PSUs)—most of which comprise a<br />
metropolitan area, a large county, or a group of smaller<br />
counties. Every PSU falls within the boundary of a state.<br />
The PSUs are then grouped into strata on the basis of independent<br />
information that is obtained from the decennial<br />
census or other sources.<br />
The strata are constructed so that they are as homogeneous<br />
as possible with respect to labor force <strong>and</strong> other<br />
1 New York City consists of Bronx, Kings, New York, Queens,<br />
<strong>and</strong> Richmond Counties.<br />
<strong>Design</strong> of the <strong>Current</strong> <strong>Population</strong> <strong>Survey</strong> Sample 3–1