Validation is tiered as shown in the pyramid below, with Tier 1 focusing on analytical sensitivity and specificity, Tier 2 broadening inclusivity and exclusivity panels for pathogen surveillance, Tier 3 emphasizing reproducibility in various laboratory settings, and Tier 4 evaluating fitness for use in international diagnostics.
Each performance characteristic is part of a larger validation scheme which varies in complexity depending on the intended use of the assay. In general, as a test is used by more people in more places, there are more variables affecting test performance that need to be anticipated and assessed. Below is an overview of how and when these validation descriptors are measured:
