Quality of quality: A diagnostic approach to qualitative evaluation

This article discusses the integration of a diagnostic lens in qualitative or mixed methods evaluations, arguing that this will improve quality: in particular, it will improve transparency, credibility and reliability of evaluation findings.We start by unpacking the notion of evaluation quality and pointing out the typical weaknesses of qualitative methods. We then introduce the basic notions of diagnostic approaches and how they relate to theory-based evaluation, process tracing, and Bayesian updating, arguing for the merits of taking a formal Bayesian approach, founded on the confusion matrix, which amongst else reduces confirmation bias and conservatism. This article draws parallels between the process tracing tests and elements of the confusion matrix.