Study Designs: Diagnostic Studies

Diagnostic tests are evolving with betterment of technology, quest for patient safety with less invasive medicine, and evolution of new diseases. It is important to assess diagnostic accuracy of a new test, and clinical impact of introduction of new test on outcomes and cost. A diagnostic study is planned for the index test based on place of new test in diagnostic pathway (screening, triage, diagnostic or add-on test) and established information of the test. A reference standard is used to classify population into diseased and healthy, and the discriminating ability of index test is measured. A sample size is calculated for expected sensitivity/specificity, margin of error and prevalence of disease in population. For dichotomous outcomes, sensitivity, specificity, predictive values and likelihood ratio are used to describe diagnostic accuracy. Efforts should be made to avoid common forms of bias including spectrum bias and partial verification bias, and blinding of observers should preferably be done.