Final Report on the Effects of Sample Attrition on Estimates of Channeling's Impacts. II. THE NATURE AND EXTENT OF ATTRITION IN THE ANALYSIS SAMPLES


The outcome measures for which channeling impacts are estimated are obtained from a variety of services. Thus, for each of the major areas of analysis in the evaluation, "analysis samples" have been defined. The analysis sample for any area is composed of that subset of the full research sample for which the necessary individual data on independent and dependent (outcome) variables are available. However, most of these analysis samples are tied closely to whether or not the sample member completed the baseline survey and the followup surveys administered 6, 12, and (for a subset of the sample) 18 months after randomization. The data sources and analysis samples are described below, followed by a comparison across treatment groups and models in the proportions of the research sample that have the data necessary for the various analyses. Total attrition rates, and reasons for attrition, are given for the samples used in the analysis of impacts at 6, 12, and 18 months after randomization. The chapter concludes with an analysis of whether the treatment and control groups available for analysis are composed of different types of individuals as a consequence of attrition.

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