Psychological Science Can Improve Diagnostic Decisions.

Diagnostic problems abound for individuals, organizations, and society. The stakes are high, often life and death. Such problems are prominent in the fields of health care, public safety, business, environment, justice, education, manufacturing, information processing, the military, and government. Particular diagnostic questions are raised repetitively, each time calling for a positive or negative decision about the presence of a given condition or the occurrence (often in the future) of a given event. Consider the following illustrations: Is a cancer present? Will this individual commit violence? Are there explosives in this luggage? Is this aircraft fit to fly? Will the stock market advance today? Is this assembly-line item flawed? Will an impending storm strike? Is there oil in the ground here? Is there an unsafe radiation level in my house? Is this person lying? Is this person using drugs? Will this applicant succeed? Will this book have the information I need? Is that plane intending to attack this ship? Is this applicant legally disabled? Does this tax return justify an audit? Each time such a question is raised, the available evidence is assessed by a person or a device or a combination of the two, and a choice is then made between the two alternatives, yes or no. The evidence may be a x-ray, a score on a psychiatric test, a chemical analysis, and so on. In considering just yes–no alternatives, such diagnoses do not exhaust the types of diagnostic questions that exist. Other questions, for example, a differential diagnosis in medicine, may require considering a half dozen or more possible alternatives. Decisions of the yes–no type, however, are prevalent and important, as the foregoing examples suggest, and they are the focus of our analysis. We suggest that diagnoses of this type rest on a general process with common characteristics across fields, and that the process warrants scientific analysis as a discipline in its own right (Swets, 1988, 1992). The main purpose of this article is to describe two ways, one obvious and one less obvious, in which diagnostic performance can be improved. The more obvious way to improve diagnosis is to improve its accuracy, that is, its ability to distinguish between the two diagnostic alternatives and to select the correct one. The less obvious way to improve diagnosis is to increase the utility of the diagnostic decisions that are made. That is, apart from improving accuracy, there is a need to produce decisions that are in tune both with the situational probabilities of the alternative diagnostic conditions and with the benefits and costs, respectively, of correct and incorrect decisions. Methods exist to achieve both goals. These methods depend on a measurement technique that separately and independently quantifies the two aspects of diagnostic performance, namely, its accuracy and the balance it provides among the various possible types of decision outcomes. We propose that together the method for measuring diagnostic performance and the methods for improving it constitute the fundamentals of a science of diagnosis. We develop the idea that this incipient discipline has been demonstrated to improve diagnosis in several fields, but is nonetheless virtually unknown and unused in others. We consider some possible reasons for the disparity between the general usefulness of the methods and their lack of general use, and we advance some ideas for reducing this disparity. To anticipate, we develop two successful examples of these methods in some detail: the prognosis of violent behavior and the diagnosis of breast and prostate cancer. We treat briefly other successful examples, such as weather forecasting and admission to a selective school. We also develop in detail two examples of fields that would markedly benefit from application of the methods, namely the detection of cracks in airplane wings and the detection of the virus of AIDS. Briefly treated are diagnoses of dangerous conditions for in-flight aircraft and of behavioral impairments that qualify as disabilities in individuals.