The Clinical Setting of an Outcome Study

The setting of a research study may or may not be the same as that of the individual patient. The evidence from a study may be unreliable when differences exist in age, sex, ethnic origin, lifestyle, prevalence of the disease in the population, or prevalence of comorbidities. Transferability of study results may also be affected by analytical variables, such as patient preparation (effects of fasting, posture, exercise, and biological variation) and method performance (accuracy and precision). 

When a new test is developed or an old test is applied to a new clinical question, users need information about the extent of agreement of the test s results with the correct diagnoses of patients. For this purpose, researchers design studies in which results from the new test are compared with the results obtained with the reference standard on the same patients. The results of the comparison can be expressed in a number of ways, including sensitivity and specificity, predictive values, likelihood ratios, diagnostic odds ratios, and areas under receiver operating characteristic (ROC) curves (see Chapter 15). We will refer to such studies as diagnostic accuracy studies. 

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