Attribute-treatment interaction research using nonexperimental data and the allocation average.

Attribute-treatment interaction (ATI) research attempts to answer the question, "Which treatment is best for whom?" Recent critical reviewers of ATI methodology have cited numerous pragmatic and methodological shortcomings of traditional experimental designs and argued that successful ATI research will require an alternative approach. This manuscript describes a purely correlational ATI method that addresses the more serious criticisms of experimental ATI research. This paper also presents use of the allocation average for ATI research that is either experimental or correlational in nature. The allocation average estimates the clinical utility of differential treatment assignment based on ATI data in terms of improved treatment outcomes. The proposed method is illustrated with hypothetical psychotherapy data and data from a recent educational study.