Advances in radiology and the real versus apparent effects of early diagnosis.

Over the last two decades, technological advances in radiology have revolutionized the practice of medicine. Although the potential benefits of these advances are well recognized, the potential harms are not. This paper describes how early diagnosis can cause overestimations of disease prevalence and the effectiveness of intervention. The paper begins by demonstrating how the observed prevalence of disease increases with the sensitivity of the test and by explaining the concept of pseudodisease. Next, the paper explains how lead time bias, length bias and overdiagnosis bias cause overestimations of the effectiveness of earlier diagnosis and associated treatments. These biases pertain to both the detection and staging of disease. In addition, the paper explains how these overestimations of disease prevalence and the effectiveness of intervention can initiate a cycle of increasing testing and treatment, which may eventually cause more harm than benefit. Finally, randomized clinical trials and decision analysis are discussed in the context of evaluating new testing strategies.