A tutorial on the validation of qualitative methods: From the univariate to the multivariate approach

• Strategies for qualitative method validation are considered.
• Univariate and multivariate qualitative methods are described.
• Performance parameters for qualitative methods are discussed.
• Cases study of qualitative methods validation is illustrated.

This tutorial provides an overview of the validation of qualitative analytical methods, with particular focus on their main performance parameters, for both univariate and multivariate methods. We discuss specific parameters (sensitivity, specificity, false positive and false negative rates), global parameters (efficiency, Youden's index and likelihood ratio) and those parameters that have a quantitative connotation since they are usually associated to concentration values (decision limit, detection capability and unreliability region).Some methodologies that can be used to estimate these parameters are also described: the use of contingency tables for the specific and global parameters and the performance characteristic curve (PCC) for the ones with quantitative connotation. To date, PCC has been less commonly used in multivariate methods.To illustrate the proposals summarized in this tutorial, two cases study are discussed at the end, one for a univariate qualitative analysis and the other for multivariate one.

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