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Evaluation of Treatment Programs

A Statistical Resolution of Selection Biases Using the Case of Problem Drinkers

University of Miami

Armand L. Mauss

Washington State University

A common and perverse problem facing those who evaluate human service programs is the difficulty in getting random assignment of clients to control and experimental groups, so that experimental or quasi-experimental research designs can be meaningfully applied. This article demonstrates the use of a technique (covariance adjustment) that statistically manipulates independent variables so as to give an approximation of random assignment on those variables. In this article, we adapt the work of Alwin and Sullivan (1976) to an actual data set from public alcohol treatment programs. We found some very significant differences between the adjusted and nonadjusted treatment out comes, demonstrating the need for some type of pretreatment controls in the absence of random assignment. The covariance adjustment technique and its assumptions are dis cussed leading to the conclusion that the technique is a very workable resolution of the random assignment problem. We also demonstrate how the technique yields some valuable information generally not available when random assignment is used: namely, the identification and weighting of certain selection biases as they relate to the dependent variable.

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