ABSTRACT
In 1928, the Illinois State Board of Parole published a study by sociologist Burgess of the parole outcome for 3,000 criminal offenders, an exhaustive sample of parolees in a period of years preceding. (In Meehl 1954a/1996, this number is erroneously reported as 1,000, a slip probably arising from the fact that 1,000 cases came from each of three Illinois prisons.) Burgess combined 21 objective factors (e.g., nature of crime, nature of sentence, chronological age, number of previous offenses) in unweighted fashion by simply counting for each case the number of factors present that expert opinion considered favorable or unfavorable to successful parole outcome. Given such a large sample, the predetermination of a list of relevant factors (rather than elimination and selection of factors), and the absence of any attempt at optimizing weights, the usual problem of cross-validation shrinkage is of negligible importance. Subjective, impressionistic, “clinical” judgments were also made by three prison psychiatrists about probable parole success. The psychiatrists were slightly more accurate than the actuarial tally of favorable factors in predicting parole success, but they were markedly inferior in predicting failure. Furthermore, the actuarial tally made predictions for every case, whereas the psychiatrists left a sizable fraction of cases undecided. The conclusion was clear that even a crude actuarial method such as this was superior to clinical judgment in accuracy of prediction. Of course, we do not know how many of the 21 factors the psychiatrists took into account; but all were available to them; hence, if they ignored certain powerful predictive factors, this would have represented a source of error in clinical judgment. To our knowledge, this is the earliest empirical comparison of two ways of forecasting behavior. One, a formal method, employs an equation, a formula, a graph, or an actuarial table to arrive at a probability, or expected value, of some outcome; the other method relies on an informal, “in the head,” impressionistic, subjective conclusion, reached (somehow) by a human clinical judge.
