Signal Detection Theory and Roc Analysis in Psychology and Diagnostics: Collected Papers

By John A. Swets | Go to book overview
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considered here, the field of aptitude testing devotes a good deal of sophisticated effort to validity questions.

What will the future bring? A basic assumption of this chapter is that testing the accuracy of diagnostic systems is often desirable and feasible and is sometimes crucial. Although individual diagnosticians are treated here only in passing, a similar case could be made for the importance of testing them. I suggest that a wider and deeper understanding of the needs and the possibilities would be beneficial in science, technology, and society, and that it is appropriate for scientists to take the lead in enhancing that understanding. Scientists might help society overcome the resistance to careful evaluation that is often shown by diagnosticians and by designers and managers of diagnostic systems, and help to elevate the national priority given to funding for evaluation efforts. Specifically, I submit that scientists can increase general awareness that the fundamental factors in accuracy testing are the same across diagnostic fields and that a successful science of accuracy testing exists. Instead of making isolated attempts to develop methods of testing for their own fields, evaluators could adapt the proven methods to specific purposes and contribute mutually to their general refinement.

The measurement of efficacy in the context of the present approach to accuracy is treated in some detail elsewhere (9, 10). The usefulness of empirical measures of diagnostic, and especially predictive, accuracy was further set in a societal context in a recent editorial: D. E. Koshland, Jr. , Science 238, 727 ( 1987).
W. W. Peterson, T. G. Birdsall, W. C. Fox, IRE Trans. Prof. Group Inf. Theorv PGIT-4, 171 ( 1954).
With a human decision-maker, one can simply give instructions to use a more or less strict criterion for each group of trials. Alternatively, one can induce a change in the criterion by changing the prior probabilities of the two events or the pattern of costs and benefits associated with the four decision outcomes. If, on the other hand, the decision depends on the continuous output of some device, say, the intraocular pressure measured in a screening examination for glaucoma, then, in different groups of trials, one simply takes successively different values along the numerical (pressure) continuum as partitioning it into two regions of values that lead to positive and negative decisions, respectively. This example of a continuous output of a system suggests the alternative to the binary procedure, namely, the so-called "rating" procedure.
Thus, to represent the strictest criterion, one takes only the trials given the highest category rating and calculates the relevant proportions from them. For the next strictest criterion, the trials taken are those given either the highest or the next highest category rating--and so on to what amounts to a very lenient criterion for a positive response. The general idea is illustrated by probabilistic predictions of rain: first, estimates of 80% or higher may be taken as positive decisions, then estimates of 60% or higher, and so on, until the pairs of true- and false-positive proportions are obtained for each of several decision criteria.
D. M. Green and J. A. Swets, Signal Detection Theorv and Psychophysics ( Wiley, New York, 1966; reprinted with updated topical bibliographies by Krieger, New York, 1974, and Peninsula Publishing, Los Altos, CA, 1988).
J. A. Swets, Science 134, 168 ( 1961); ibid. 182, 990 ( 1973). See Chapter 1.


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