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National Evaluation of Welfare-to-Work Strategies: 2-Year Client Survey Files: Background Information on Selection of the 2-Year Client Survey Sample

 Background Information on Selection of the 2-Year Client Survey Sample   Data on participation, degree receipt, job quality, income, transitional benefits, health care coverage, child care, child outcomes, and several other measures used in this report come from the Two-Year Client Survey.  The survey was administered to a subsample of the full research sample approximately two years after random assignment.  Key analysis samples  The survey eligible sample ("eligibles"). Sample members in the full research sample who were randomly assigned during months in which the survey sample was selected and who met the criteria for inclusion.  The fielded sample ("fieldeds"). Members of the eligible sample who were chosen to be interviewed.  The respondent sample ("respondents"). Members of the eligible sample, chosen to be interviewed (i.e., fieldeds), who were interviewed.  The non-respondent sample ("non-respondents"). Members of the eligible sample, chosen to be interviewed (i.e., fieldeds), who were not interviewed. They either could not be located or declined to be interviewed.    I.  Survey Selection and Sampling Ratios  Several of the chapters in this report analyze program impacts calculated from survey responses as well as impacts calculated from administrative records for the full sample. It is important to understand the process by which the survey samples were chosen and survey responses collected in order to assess the comparability of these results.  Selecting the Eligible Sample  In all sites, the survey eligible sample includes members of the full research sample who were randomly assigned during some, but not all, months of sample intake (See SAMTBL1.TXT). Limiting the eligible sample in this way can introduce "cohort effects," impact estimates that are especially large or small for sample members randomly assigned during particular months. A cohort effect may occur because members of the survey eligible sample differ in measured or unmeasured background characteristics from persons randomly assigned in other months. Changes in area labor markets or in program implementation that occur at some point after the start-up of random assignment may also introduce cohort effects - e.g., by increasing or decreasing a program's relative success in moving welfare recipients from welfare to work. These issues are most germane to Columbus, Detroit, Portland, and Oklahoma City, where selection of the survey eligible samples took place over fewer months than in Atlanta, Grand Rapids, and Riverside.  Further, the research strategy for choosing the survey eligible samples in Atlanta, Grand Rapids, and Riverside required exclusion of sample members with certain background characteristics:  teen parents; parents with children less than 3 years old; men with children ages 3 to 5; people who did not speak either English or Spanish; and people who did not provide information on their educational status and children's ages prior to random assignment. This selection strategy may affect the generalizability of impact results recorded from the survey.  Fortunately, cohort effects were small. For instance, differences in two-year earnings gains between the full research samples and the survey eligible samples varied by less than $100 in 9 of the 11 programs and by less than $200 in every program (results not shown).   Selecting the Fielded Sample  The percentage of the survey eligibles who were chosen for the fielded sample is the sampling ratio. Across all sites, sampling ratios ranged from 15 percent to 100 percent.  In four sites, Atlanta, Grand Rapids, Portland, and  Riverside, the fielded sample was selected by drawing a stratified random subsample of the survey eligible sample. In Atlanta, Grand Rapids, and Riverside, the sampling ratio varied (for research purposes) by research group, date of random assignment, age of youngest child, and pre-random assignment educational attainment of the sample member. In Portland, sampling ratios varied by research groups and by date of random assignment only. Although corrected for, as discussed below, differences in sampling ratios may also affect survey impact estimates. For instance, unless the total sample size is large, different sampling ratios increase the likelihood that persons chosen in one research group differ (perhaps in unmeasured characteristics) from persons chosen in another research group.  In two other sites, Detroit and Oklahoma City, the fielded sample for program and control group members was selected by drawing a simple random sample from the eligible sample. That is, within these sites, a single sampling ratio was applied to all program and control group members, irrespective of their background characteristics. This sampling strategy was used in Columbus as well, except that the sampling ratio for control group members was slightly higher than for members of the Integrated and Traditional groups.   II.  Weighting  To estimate impacts, weights were applied to the survey respondent sample to correct for differences in sampling ratios between the strata in Atlanta, Grand Rapids, Portland, and Riverside. In the unweighted fielded survey sample in these sites, strata (i.e., sample members who share background characteristics and have the same sampling ratio) with high sampling ratios are over-represented and strata with low sampling ratios are under-represented. To make the fielded sample more closely replicate the background characteristics of survey eligibles, weights for each stratum were set to equal the inverse of the sampling ratio for that stratum. For example, a stratum in which 1 in 4 eligible persons were chosen would receive a weight of 4 (or 4/1), whereas a stratum in which every eligible person was chosen would receive a weight of 1 (or 1/1). THE SAME WEIGHTS ARE USED FOR THE RESPONDENT SAMPLE. Weighting was not required for sample members in Columbus, Detroit, and Oklahoma City, because sample members' background characteristics did not affect their chances of selection.   The variable FIELDWGT stores the weight value for each respondent.  It should be noted that under some conditions impacts for a weighted respondent sample may still be different from those for the eligible sample. For example, this result could occur if very different proportions of program and control group fieldeds answered the survey, or if members of a subgroup within one research group were more likely to be interviewed than their counterparts in a different research group.   III.  Response Rates  As noted above, sample members who were fielded and interviewed are survey respondents. Those chosen to be surveyed but who were not interviewed are non-respondents. The table below shows the response rate, the percentage of the fielded sample who responded to the survey, by program and research group. As shown, in most programs, response rates are high enough to suggest that the survey probably represents the eligible sample.  The goal of the survey effort was to obtain responses from at least 70 percent of the fielded sample. The 70 percent goal was achieved for all research groups in all sites; in fact, response rates reached 80 percent or above for most research groups. These results inspire particular confidence in the impacts for respondents.              National Evaluation of Welfare-to-Work Strategies              Number of Fielded Survey Sample Members and                   Two-Year Client Survey Response Rates                                                Number of                                               Fielded     Response Site and Program                              Members     Rate (%)  Atlanta Labor Force Attachment                 908         88.5 Atlanta Human Capital Development             1225         90.9 Atlanta Control                               1200         90.5  Grand Rapids Labor Force Attachment            637         90.1 Grand Rapids Human Capital Development         647         88.7 Grand Rapids Control                           631         92.6  Riverside Labor Force Attachment               740         76.2 Riverside Human Capital Development            819         75.8 Riverside Control                             1396         79.8  Columbus Integrated                            455         81.5 Columbus Traditional                           459         79.7 Columbus Control                               460         77.6  Detroit Program                                261         80.5 Detroit Control                                259         83.4  Oklahoma City Program                          356         72.8 Oklahoma City Control                          360         70.0  Portland Program                               385         77.1 Portland Control                               377         83.0