Sensitivity, Specificity, and Predictive Values in the 'Sensitivity and Specificity of Clinical Diagnostics'

To the Editor.— The measures of accuracy in clinical screening or diagnosis relate to the intrinsic ability of a procedure to identify correctly those persons with disease (sensitivity) and those persons without disease (specificity).1In a recent article entitled "The Sensitivity and Specificity of Clinical Diagnostics During Five Decades,"2the authors use theterms clinical accuracy for a positive diagnosis and clinical accuracy for a negative diagnosisand equate them by definition to the positive predictive value (the proportion of positive tests or diagnoses that correctly identify the presence of disease) and the negative predictive value (the proportion of negative tests that correctly identify the absence of disease), respectively. Unlikesensitivity and specificity, the predictive values are not properties inherent to the procedure itself, but vary with the prevalence of disease in the population tested. For example, the authors state that "the accuracy of the clinical diagnosis