Using the Current Population Survey CPS in Social Science Research

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Using the Current Population Survey (CPS) in
Social Science Research
Wei Sun College of Arts and Letters University of
Notre Dame
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Why Use the CPS?

• 1. Up to date annual data can be used between
  two Decennial Censuses
• 2. Diversity diverse information on the labor
  force, demographics, and other specific topics
• 3. Popularity Primary source of monthly
  estimates of total employment, self-employed
  persons, domestic and unpaid workers, wage
  workers, and unemployment widely used by
  researchers
• 4. Reliability large and nationally
  representative sample for generating reliable
  statistical inference

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Major Social Science Data Sets Used by Journal
Articles
Source ICPSR
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CPS Overview

• The CPS is a monthly survey conducted by the
  Bureau of the Census for the Bureau of Labor
  Statistics.
• The CPS is a probability sample designed to
  produce national and state estimates of labor
  force characteristics and demographic status of
  the civilian, non-institutional population 16
  years of age and older.

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Overview (continued)

• The CPS samples housing units from lists of
  addresses obtained from the Decennial Census of
  population and housing.
• A housing unit is interviewed for 4 consecutive
  months, then dropped from the sample for the next
  8 months, then interviewed for 4 more months.
• Each month has eight rotation groups. This method
  is a compromise between a permanent sample and a
  completely new sample.

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Locating Information on Survey Design

• Details about survey design can be found in CPS
  Technical Paper 63RV, 2002. Please visit the
  Census Bureaus web site to locate the report at
  
• http//www.census.gov/prod/2002pubs/tp63rv.pdf

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Delivery Format

• Monthly Current Population Survey
• Basic monthly data including demographic and
  labor force data
• CPS Supplements
• March CPS- Annual Social and Economic Supplement
  Includes annual data on income, work experience,
  non-cash benefits, and migration

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Delivery Format (continued)

• Other Supplements
• January displaced workers, tenure, mobility
• February contingent workers
• April child support
• May tobacco use, work schedules
• June fertility
• August job training
• September volunteers
• October school enrollment
• November voting and registration
• December food security

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Accessing CPS Data Programming Skills Required

• 1. http//www.census.gov/cps/
• Download raw data and extract data with
  statistical software
• 2. http//www.nber.org/
• From 1992-2006
• Data sets, document files, and extraction
  programs
• 3. IPUMS-CPS
• http//cps.ipums.org/cps/index.shtml

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Accessing CPS Data Less Programming Skills
Required

• Data Ferrett http//dataferrett.census.gov/
• A data search engine created by the Census Bureau
  and the BLS
• Includes March CPS back to 1992 and other
  supplements
• Dont need to create extraction program, data can
  be downloaded in your preferred format
• Can tabulate several types of data
• Easy for undergraduate students to use

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The Sample Size

• March 2005 CPS Supplement
• Over 600 Variables
• Total Records 396,461
• 98,664 Household Records
• 87,147 Family Records
• 210,648 Person Records

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The Raw Data Structure

• The CPS is delivered as a hierarchical raw data
  file with three levels
• Household
• Family
• Person

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Illustration of Record Sequence

• Household 2 (2 families)
• Family 1 variables
• Person 1 variables
• Person 2 variables
• Family 2 variables
• Person 1 variables
• Person 2 variables
• Person 3 variables

• Household 1 (1 family)
• Family 1 variables
• Person 1 variables
• Person 2 variables
• Person 3 variables

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Importing Raw Data

• The CPS March file has three record types.
• The value in column 1 indicates what
• record type the line is.
• Importing raw data is a process of
• converting hierarchical data to
• rectangular data.
• SAS, SPSS, and Stata programs
• are available at www.nber.org

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Output in SAS Hierarchical Nature of Data File
Reflected in Rectangular Format
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Sample Weight Variables

• Household weight
• Family weight
• Final weight
• Earnings weight
• March supplement weight

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Major Household Variables

• Household type
• Economic (Income and non-cash benefits)
• Housing characteristics
• Geographic variables

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Major Family Variables

• Family type
• Family structure
• Family income (poverty level, source of income,
  non-cash benefits)

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Major Person Variables

• Family Interrelationship
• Core Demographic
• Race and Ethnicity
• Education
• Labor Force
• Income
• Migration
• Health Insurance

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CPS Compared to the American Community Survey
(ACS) PUMS

• CPS has smaller sample Unable to produce
  reliable single-year estimates for some states or
  sub-state areas
• CPS is better source of official national
  estimates of poverty
• Some questions are similar and overlap
• CPS is the primary source of information about
  national trends in the family
• CPS collects more than 50 sources of income
  including non-cash benefits while ACS only
  includes 8 sources

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CPS Compared to the Survey of Income and
Program Participation (SIPP)

• Both collect similar information on income
  source, labor force, and program participation.
  SIPP has more information on assets and
  liabilities
• CPS panel duration is shorter than SIPP, SIPP
  follows people across waves while CPS does not
• March CPS Sample is larger than SIPP
• SIPP over-samples low income households, CPS is
  less biased
• Detailed comparisons are based on research
  questions.

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How CPS Data is Used in Research By Method

• 1. Cross sectional analysis (single cross
  section)
• Mostly commonly used research method
• 2. Time series aggregate analysis for long-term
  trends
• Example Sources of Health Insurance and
  Characteristics of the Uninsured.
• http//www.ebri.org/pdf/briefspdf/EBRI_IB_10a-2006
  1.pdf

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How CPS Data is Used in Research Pooling CPS
Data

• 3. Pooling the March CPS Across Years
• Why pool CPS data?
• Increases sample size, especially for studying
  minorities, immigrants, single families, and
  other population subgroups.
• Research example
• Farley, Reynolds and Richard Alba. The New
  Second Generation in the United States.
  International Migration Review. Vol. 36. No. 3
  (Fall 2002).

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How CPS Data is Used in Research Pooling CPS
Data (continued)

• Warnings
• 1. When pooling two consecutive years, more than
  50 percent of the sample is overlapped.
• 2. Some variable names and value intervals change
  from year to year (see next slide)
• Get pooled CPS data from IPUMS
• http//cps.ipums.org/cps/index.shtml

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Example of Changed Variables Across Years
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How CPS Data is Used in Research Matching CPS
Data

• 4. Matching the March CPS Supplement
  (Longitudinal Aspect)
• Why match CPS data?
• To study short-term dynamics, e.g. the length of
  an unemployment spell
• To utilize CPS address based sample design
• Example Foreign Born Emigration A New Approach
  and Estimates Based on Matched CPS Files.
  Jennifer van Hook, Weiwei Zhang, Frank Bean, and
  Jeffery Passel. Demography. Vol. 43. No. 2 (May
  2006).

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How CPS Data is Used in Research Matching CPS
Data (continued)

• The CPS is not good for matching because
• 1. 50 percent of the sample is lost when matching
  two consecutive years of data
• 2. Duration of the sample is short, limiting
  longitudinal nature
• 3. Demographic changes make matching more
  complicated and decrease the sample size
• 4. There are tradeoffs in merging merge
  individuals who should merge with merging
  individuals who shouldnt.

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How CPS Data is Used in Research Matching CPS
Data (continued)

• Basic (simple) approach
• Household ID, Household line number, Person line
  number
• Madrian and Lefgan approach
• Basic merge first
• Delete observations that sex, race, or age do not
  match after basic merge
• Source An Approach to Longitudinally Matching
  CPS Respondents. Madrian, Brigitte and Lars John
  Lefgan. Journal of Economic and Social
  Measurement. Vol. 26 (2000).

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How CPS Data is Used in Research By Research
Area

• 1. Policy Research
• The CPS provides the government with
• Monthly estimates of labor force characteristics
  and the general demographic composition of the
  population.
• Important indicators for planning and evaluating
  government programs
• Related publications
• Bureau of Labor Statistics, Monthly Labor Review
• Bureau of Census, Current Population Report

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How CPS Data is Used in Research By Research
Area (continued)

• 2. Community Research
• Study immigrants (immigration policy, education,
  political participation), local state policy on
  minimum wage, health insurance.
• Conduct research with community partners to
  promot justice and equity in a diverse,
  multiethnic, multicultural world.

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How CPS Data is Used in Research Academic
Research

• 3. Selected topics using CPS data
• Demographics Living arrangement, marriage, child
  support, population change, race and ethnicity,
  gender, and undocumented population
• Education Grade distribution, economic returns
  to education, school enrollment, income gap
  between high and low education levels
• Health insurance and employee benefits
  Characteristics of uninsured people, pensions,
  health insurance for children

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Academic Research Selected Topics Using CPS
Data (continued)

• Income and poverty Earnings mobility, earnings
  inequality, income distribution, minimum wage,
  poverty
• Labor force Employment instability, job
  mobility, part-time work force, at-home work
  force, youth employment
• Health Insurance, fertility, tobacco use,
  smoking policy, food security
• Voting/election can be used to study voting
  participation among immigrants and across
  immigration generations

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Academic Research Selected Topics Using CPS
Data (continued)

• Immigration The CPS is a major data source for
  studying immigration
• CPS surveys have questions on
• Nativity
• Parental Nativity
• Citizenship
• Year of entry
• Main reason for moving
• Topics include
• Estimation of undocumented immigration
• The effect of immigrants on the economy
• Characteristics of the foreign born, etc.

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Accessing Literature that Utilizes CPS Data

• http//www.icpsr.umich.edu/ICPSR/citations/index.h
  tml
• Type CPS or Current Population Survey in the
  search field under Search the Bibliography of
  Data-Related Literature
• This is a tool to train students how to do
  research
• http//bibliography.ipums.org/

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Journals that Published Papers Using CPS Data
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Journals that Published Papers Using CPS Data
(continued)
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Want to Learn More?

• Please contact
• Wei Sun
• Office 945 Flanner Hall
• Telephone [phone]
• Email wei.sun.7_at_nd.edu