The association must be verified statistically by a large number of independent observations in multiple families. The observations must be independently replicated and subject to peer review. Consequently, analytic validity is the probability that the measured value will be within a predefined range of the true activity or concentration. In validating a new test analytically, the laboratory techniques should be as similar as possible to those in laboratories that will be performing the test clinically once it is validated. Analytical sensitivity and specificity must be determined before tests are made available in clinical practice.
Predictive value depends on the prevalence of the disease in the group or population being studied.
Two intrinsic features of genetic diseases affect results. Heterogeneity reduces the clinical sensitivity, and incomplete penetrance reduces predictive value of a positive test result. Current technology may not be able to detect all disease-related alleles, particularly when there are many of them, which is often the case. This failure to detect all disease-related mutations reduces a test's clinical sensitivity. In clinical validation, the study sample must be drawn from a group of subjects representative of the population for whom the test is intended.