This chapter contains sections titled: Introduction What do you mean by “normal” and “the normal range”? The question is everything Phase I questions: Do patients with the target disorder have different test results from normal individuals? Phase II questions: Are patients with certain test results more likely to have the target disorder than patients with other test results? Phase III questions: Among patients in whom it is clinically sensible to suspect the target disorder, does the level of the test result distinguish those with and without the target disorder? Threats to the validity of Phase III studies Limits to the applicability of Phase III studies Phase IV questions: Do patients who undergo this diagnostic test fare better (in their ultimate health outcomes) than similar patients who do not? Phase V questions: Does use of the diagnostic test lead to better health outcomes at an acceptable cost? References Introduction What do you mean by “normal” and “the normal range”? The question is everything Phase I questions: Do patients with the target disorder have different test results from normal individuals? Phase II questions: Are patients with certain test results more likely to have the target disorder than patients with other test results? Phase III questions: Among patients in whom it is clinically sensible to suspect the target disorder, does the level of the test result distinguish those with and without the target disorder? Threats to the validity of Phase III studies Limits to the applicability of Phase III studies Phase IV questions: Do patients who undergo this diagnostic test fare better (in their ultimate health outcomes) than similar patients who do not? Phase V questions: Does use of the diagnostic test lead to better health outcomes at an acceptable cost? References