The Role of Prevalence Rates, Sensitivity, and Specificity in Assessment Accuracy

A little discussed issue for practitioners is the probability that a client actually has (or does not have) a disorder that he or she has been diagnosed as having (or not having). These probabilities depend upon the sensitivity and specificity of the assessment procedure used, and on the prevalence of the disorder among those seeking services. Probability theory is used in this article to demonstrate that in many, if not most cases, these probabilities will be quite low and that the likelihood of misdiagnosis will be high. The implications of these findings for assessment in social work practice are discussed.