Current Population Survey (CPS)

Transcription

1 Current Population Survey (CPS) 1 Background The Current Population Survey (CPS), sponsored jointly by the U.S. Census Bureau and the U.S. Bureau of Labor Statistics (BLS), is the primary source of labor force statistics for the population of the United States. The CPS is the source of numerous high-profile economic statistics, including the national unemployment rate, and provides data on a wide range of issues relating to employment and earnings. The CPS is administered by the Census Bureau using a probability selected sample of about 60,000 occupied households.1 The fieldwork is conducted during the calendar week that includes the 19th of the month. The questions refer to activities during the prior week; that is, the week that includes the 12th of the month. Households from all 50 states and the District of Columbia are in the survey for 4 consecutive months, out for 8, and then return for another 4 months before leaving the sample permanently. This design ensures a high degree of continuity from one month to the next (as well as over the year). The sampling scheme has the added benefit of allowing the constant replenishment of the sample without excessive burden to respondents. The CPS questionnaire is a completely computerized document that is administered by Census Bureau field representatives across the country through both personal and telephone interviews. Additional telephone interviewing is conducted from the Census Bureaus three centralized collection facilities in Hagerstown, Maryland; Jeffersonville, Indiana; and Tucson, Arizona. To be eligible to participate in the CPS, individuals must be 15 years of age or over and not in the Armed Forces. People in institutions, such as prisons, long-term care hospitals, and nursing homes are ineligible to be interviewed in the CPS. In general, the BLS publishes labor force data only for people aged 16 and over, since those under 16 are limited in their labor market activities by compulsory schooling and child labor laws. No upper age limit is used, and full-time students are treated the same as nonstudents. One person generally responds for all eligible members of the household. The person who responds is called the reference person and usually is the person who either owns or rents the housing unit. If the reference person is not knowledgeable about the employment status of the others in the household, attempts are made to contact those individuals directly. In addition to the regular labor force questions, the CPS often includes supplemental questions on subjects of interest to labor market analysts. These include annual work activity and income, veteran status, school enrollment, contingent employment, worker displacement, and job tenure, among other topics. Because of the surveys large sample size and broad population coverage, a wide range of sponsors use the CPS supplements to collect data on topics as diverse as expectation of family size, tobacco use, computer use, and voting patterns. 2 Survey Design The CPS sample is a multistage stratified sample of approximately 72,000 assigned housing units from 824 sample areas designed to measure demographic and labor force characteristics of the civilian noninstitutionalized population 16 years of age and older. Approximately 12,000 of the assigned housing units are sampled under the State Childrens Health Insurance Program (SCHIP) expansion that has been part of the official CPS sample since July The CPS samples housing 1

2 units from lists of addresses obtained from the 2000 Decennial Census of Population and Housing. The sample is updated continuously for new housing built after Census The first stage of sampling involves dividing each U.S. state into primary sampling units (PSUs), most of which comprise a metropolitan area, a large county, or a group of smaller adjacent counties. The CPS consists of independent samples in each state and the District of Columbia. Within each state, the PSUs are grouped into homogenous strata with respect to labor force and other social and economic characteristics that are highly correlated with unemployment. One PSU is sampled per stratum, where the probability of selection for each PSU in the stratum is proportional to its population. In the second stage of sampling, a systematic sample of housing units is drawn from within each chosen PSU. Addresses for housing units are taken from sources such as lists of addresses obtained from the decennial censuses and building permits. Ultimate sampling units (USUs) are clusters of about four housing units. Usually, all households in the USU are in the sample. Occasionally, a third stage of sampling is necessary when actual USU size is extremely large. The multi-stage stratified sampling method is roughly equivalent to dividing the entire United States into USUs and selecting a clustered sample of these USUs for interviewing. Hence, the CPS sample is also a cluster sample. 3 First Stage of the Sample Design The first stage of the CPS sample design is the selection of counties. The purpose of selecting a subset of counties instead of having all counties in the sample is to minimize the cost of the survey. This is done mainly by minimizing the number of field representatives needed to conduct the survey, and reducing the travel cost incurred in visiting the sample housing units. Two features of the first-stage sampling are: (1) to ensure that sample counties represent other counties with similar labor force characteristics that are not selected and (2) to ensure that each field representative is allotted a manageable workload in his or her sample area. The first-stage sample selection is carried out in three major steps: 1. Definition of the PSUs. 2. Stratification of the PSUs within each state. 3. Selection of the sample PSUs in each state. 3.1 Definition of the Primary Sampling Units PSUs are delineated so that they encompass the entire United States. The land area covered by each PSU is made reasonably compact so it can be traversed by an interviewer without incurring unreasonable costs. The population is as heterogeneous with regard to labor force characteristics as can be made consistent with the other constraints. Strata are constructed that are homogenous in terms of labor force characteristics to minimize between- PSU variance. Between-PSU variance is a component of total variance that arises from selecting a sample of PSUs rather than selecting all PSUs. In each stratum, a PSU is selected that is representative of the other PSUs in the same stratum. When revisions are made in the sample each decade, a procedure used for reselection of PSUs maximizes the overlap in the sample PSUs with the previous CPS sample. Most PSUs are groups of contiguous counties rather than single counties. A group of counties is more likely than a single county to have diverse labor force characteristics. Limits are placed on the geographic size of a PSU to contain the distance a field representative must travel. 2

3 3.2 Rules for Defining PSUs 1. Each PSU is contained within the boundary of a single state. 2. Metropolitan statistical areas (MSAs) are defined as separate PSUs using projected 2003 Core-Based Statistical Area (CBSA) definitions. CBSAs are defined as metropolitan or micropolitan areas and include at least one county. Micropolitan areas and areas outside of CBSAs are considered nonmetropolitan areas. If any metropolitan area crosses state boundaries, each state-metropolitan area intersection is a separate PSU. 3. For most states, PSUs are either one county or two or more contiguous counties. In some states, county equivalents are used: cities, independent of any county organization, in Maryland, Missouri, Nevada, and Virginia; parishes in Louisiana; and boroughs and census divisions in Alaska. 4. The area of the PSU should not exceed 3,000 square miles except in cases where a single county exceeds the maximum area. 5. The population of the PSU is at least 7,500 except where this would require exceeding the maximum area specified in number In addition to meeting the limitation on total area, PSUs are formed to limit extreme length in any direction and to avoid natural barriers within the PSU. 3.3 Stratification of Primary Sampling Units The CPS sample design calls for combining PSUs into strata within each state and selecting one PSU from each stratum. For this type of sample design, sampling theory and cost considerations suggest forming strata with approximately equal population sizes. When the design is self-weighting (same sampling fraction in all strata) and one field representative is assigned to each sample PSU, equal stratum sizes have the advantage of providing equal field representative workloads (at least during the early years of each decade, before population growth and migration significantly affect the PSU population sizes). The objective of the stratification, therefore, is to group PSUs with similar characteristics into strata having approximately equal populations in Sampling theory and costs dictate that highly populated PSUs should be selected for sample with certainty. The rationale is that some PSUs exceed or come close to the population size needed for equalizing stratum sizes. These PSUs are designated as self-representing (SR); that is, each of the SR PSUs is treated as a separate stratum and is included in the sample. The following describes the steps for stratifying PSUs for the 2000 redesign: 1. A PSU which consists of at least one county that is likely to be part of the 151 most populous metropolitan areas based on projected definitions and Census 2000 population is required to be SR. 2. The remaining PSUs are grouped into non-self- representing (NSR) strata within state boundaries. In each NSR stratum, one PSU will be selected to represent all of the PSUs in the stratum. They are formed by adhering to the following criteria: (a) Roughly equal-sized NSR strata are formed within a state. 3

4 (b) NSR strata are formed so as to yield reasonable field representative workloads in an NSR PSU of roughly 35 to 55 housing units. The number of NSR strata in a state is a function of the 2000 population, civilian labor force, state CV, and between-psu variance4 on the unemployment level. (Workloads in NSR PSUs are constrained because one field representative must canvass the entire PSU. No such constraints are placed on SR PSUs.) In Alaska, the strata are also a function of expected interview cost. (c) NSR strata are formed with PSUs homogeneous with respect to labor force and other social and economic characteristics that are highly correlated with unemployment. This helps to minimize the between-psu variance. (d) Stratification is performed independently of previous CPS sample designs. Key variables used for stratification are: Number of males unemployed. Number of females unemployed. Number of families with female head of household. Ratio of occupied housing units with three or more people, of all ages, to total occupied hous- ing units. In addition to these, a number of other variables, such as industry and wage variables obtained from the Bureau of Labor Statistics, are used for some states. The number of stratification variables in a state ranges from 3 to 7. (e) In states with SCHIP sample, the self-representing PSUs are the same for both CPS and SCHIP In most. states, the same non-self-representing sample PSUs are in sample for both surveys. However, to improve the reliability of the SCHIP estimates in Maine, Maryland, and Nevada, the SCHIP non- self-representing PSUs are selected independent of the CPS sample PSUs, with replacement. The methodology for the stratification of PSUs for SCHIP in these states is similar to the other stratifications, except that the stratification variable used is the number of people under age 18 with a household income below 200 percent of poverty. 3.4 Selection of Sample Primary Sampling Units Each SR PSU is in the sample by definition. There are currently 446 SR PSUs. In each of the remaining 378 NSR strata, one PSU is selected for the sample following the guidelines described next. Four of the NSR strata only contain SCHIP sample. At each sample redesign of the CPS, it is important to minimize the cost of introducing a new set of PSUs. Substantial investment has been made in hiring and training field representatives in the existing sample PSUs. For each PSU dropped from the sample and replaced by another in the new sample, the expense of hiring and training a new field representative must be accepted. Furthermore, there is a temporary loss in accuracy of the results produced by new and relatively inexperienced field representatives. Concern for these factors is reflected in the procedure used for selecting PSUs. 4 Second Stage of the Sample Design The second stage of the CPS sample design is the selection of sample housing units within PSUs. The objectives of within-psu sampling are to: 4

5 1. Select a probability sample that is representative of the civilian noninstitutionalized population. 2. Give each housing unit in the population one and only one chance of selection, with virtually all housing units in a state or substate area having the same overall chance of selection. 3. For the sample size used, keep the within-psu variance on labor force statistics (in particular, unemploy- ment) at as low a level as possible, subject to respondent burden, cost, and other constraints. 4. Select within-psu sample units for additional samples that will be needed before the next decennial census. 5. Put particular emphasis on providing reliable estimates of monthly levels and change over time of labor force items. USUs are the sample units selected during the second stage of the CPS sample design. As discussed earlier in this chapter, most USUs consist of a geographically compact cluster of approximately four addresses, correspond- ing to four housing units at the time of the census. Use of housing unit clusters lowers travel costs for field representatives. Clustering slightly increases within-psu variance of estimates for some labor force characteristics since respondents within a compact cluster tend to have similar labor force characteristics. 5 Questionnaire Concepts and Definitions 5.1 INTRODUCTION An important component of the Current Population Survey (CPS) is the questionnaire, also called the survey instrument. The survey instrument utilizes automated data col- lection methods; that is, computer-assisted personal interviewing (CAPI) and computer-assisted telephone interviewing (CATI). This chapter describes and discusses its concepts, definitions, and data collection procedures and protocols. 5.2 STRUCTURE OF THE SURVEY INSTRUMENT The CPS interview is divided into three basic parts: (1) household and demographic information, (2) labor force information, and (3) supplement information. Supplemental questions are added to the CPS in most months and cover a number of different topics. The order in which interviewers attempt to collect information is: (1) housing unit data, (2) demographic data, (3) labor force data, (4) more demographic data, (5) supplement data, and finally (6) more housing unit data. The concepts and definitions of the household, demo- graphic, and labor force data are discussed below. 5.3 CONCEPTS AND DEFINITIONS Household and Demographic Information Upon contacting a household, interviewers proceed with the interview unless the case is a definite noninterview. (Chapter 7 discusses the interview process and explains refusals and other types of noninterviews.) When interviewing a household for the first time, interviewers collect information about the housing unit and all individuals who usually live at the address. 5

6 Housing unit information. Upon first contact with a housing unit, interviewers collect information on the housing units physical address, its mailing address, the year it was constructed, the type of structure (single or multiple family), whether it is renter- or owner-occupied, whether the housing unit has a telephone and, if so, the telephone number. Household roster. After collecting or updating the housing unit data, the interviewer either creates or updates a list of all individuals living in the unit and determines whether or not they are members of the household. This list is referred to as the household roster. Household respondent. One person may provide all of the CPS data for the entire sample unit, provided that the person is a household member 15 years of age or older who is knowledgeable about the household. The person who responds for the household is called the household respondent. Information collected from the household respondent for other members of the household is referred to as proxy response. Reference person. To create the household roster, the interviewer asks the household respondent to give the names of all persons living or staying in the housing unit, and to start with the name of the person or one of the persons who owns or rents the unit. The person whose name the interviewer enters on line 1 (presumably one of the individuals who owns or rents the unit) becomes the reference person. The household respondent and the reference person are not necessarily the same. For example, if you are the household respondent and you give your name first when asked to report the household roster, then you are also the reference person. If, on the other hand, you are the household respondent and you give your spouses name first when asked to report the household roster, then your spouse is the reference person. Household. A household is defined as all individuals (related family members and all unrelated individuals) whose usual place of residence at the time of the interview is the sample unit. Individuals who are temporarily absent and who have no other usual address are still classified as household members even though they are not present in the household during the survey week. College students compose the bulk of such absent household members, but people away on business or vacation are also included. (Not included are individuals in institutions or the military.) Once household/nonhousehold membership has been established for all people on the roster, the interviewer proceeds to collect all other demographic data for household members only. Relationship to reference person. The interviewer will show a flash card with relationship categories (e.g., spouse, child, grandchild, parent, brother/sister) to the household respondent and ask him/her to report each household members relationship to the reference person (the person listed on line one). Relationship data also are used to define families, subfamilies, and individuals whose usual place of residence is elsewhere. A family is defined as a group of two or more individuals residing ogether who are related by birth, marriage, or adoption; all such individuals are considered members of one family. Families are further classified either as married-couple families or as families maintained by women or men with- out spouses present. Subfamilies are defined as families that live in housing units where none of the members of the family are related to the reference person. A house- hold may contain unrelated individuals; that is, people who are not living with any relatives. An unrelated indi- vidual may be part of a household containing one or more families or other unrelated individuals, may live alone, or may reside in group quarters, such as a rooming house. 6

7 Questions for Employed and Unemployed 1. Does anyone in this household have a business or a farm? 2. LAST WEEK, did you do ANY work for (either) pay (or profit)? Parenthetical filled in if there is a business or farm in the household. If 1 is yes and 2 is no, ask 3. If 1 is no and 2 is no, ask LAST WEEK, did you do any unpaid work in the family business or farm? iif 2 and 3 are both no, ask LAST WEEK, (in addition to the business) did you have a job, either full-or part-time? Include any job from which you were temporarily absent. Parenthetical filled in if there is a business or farm in the household. If 4 is no, ask LAST WEEK, were you on layoff from a job? If 5 is yes, ask 6. If 5 is no, ask Has your employer given you a date to return to work? If no, ask Have you been given any indication that you will be recalled to work within the next 6 months? If no, ask Have you been doing anything to find work during the last 4 weeks? If yes, ask What are all of the things you have done to find work during the last 4 weeks? Individuals are classified as employed if they say yes to questions 2, 3 (and work 15 hours or more in the reference week or receive profits from the business/farm), or 4. Individuals who are available to work are classified as unemployed if they say yes to 5 and either 6 or 7, or if they say yes to 8 and provide a job search method that could have brought them into contact with a potential employer in 9. 7