Major Contribution The Meta-Analysis of Clinical Judgment Project: Fifty-Six Years of Accumulated Research on Clinical Versus Statistical Prediction

Clinical predictions made by mental health practitioners are compared with those using statistical approaches. Sixty-seven studies were identified from a comprehensive search of 56 years of research; 92 effect sizes were derived from these studies. The overall effect of clinical versus statistical prediction showed a somewhat greater accuracy for statisti-cal methods. The most stringent sample of studies, from which 48 effect sizes were extracted, indicated a 13 % increase in accuracy using statistical versus clinical methods. Several variables influenced this overall effect. Clinical and statistical prediction accu-racy varied by type of prediction, the setting in which predictor data were gathered, the type of statistical formula used, and the amount of information available to the clinicians and the formulas. Recommendations are provided about when and under what conditions counseling psychologists might use statistical formulas as well as when they can rely on clinical methods. Implications for clinical judgment research and training are discussed. A large portion of a counseling psychologist’s work involves deciding what information to collect about clients and, based on that information, predicting future client outcomes. This decision making can occur both at the microlevel, such as moment-to-moment decisions in a counseling session, and at the macrolevel, such as predictions about outcomes such as suicide risk, violence, and response to treatment (Spengler, Strohmer, Dixon, & Shivy, 1995). Because the quality of client care is often determine