Validating Qualitative Diagnostic Tests (575 Patients)

Abstract

Clinical trials of disease management require accurate tests for making a diagnosis/ patient follow-up. Whatever test, screening, laboratory or physical, investigators involved need to know how good it is. The goodness of a diagnostic test is a complex question that is usually estimated according to three criteria: (1) its reproducibility, (2) precision, and (3) validity. Reproducibility is synonymous to reliability, and is, generally, assessed by the size of differences between duplicate measures. Precision of a test is synonymous to the spread in the test results, and can be estimated, e.g., by standard deviations / standard errors. Validity is synonymous to accuracy, and can be defined as a test’s ability to show which individuals have the disease in question and which do not. Unlike the first two criteria, the third is hard to quantify, first, because it is generally assessed by two estimators rather than one, namely sensitivity and specificity, defined as the chance of a true positive and true negative test, respectively.