  Because experiment/model comparisons in magnetic confinement fusion have not
yet satisfied the requirements for validation as understood broadly, a set of
approaches to validating mathematical models and numerical algorithms are
recommended as good practices. Previously identified procedures, such as
verification, qualification, and analysis of error and uncertainty, remain
important. However, particular challenges intrinsic to fusion plasmas and
physical measurement therein lead to identification of new or less familiar
concepts that are also critical in validation. These include the primacy
hierarchy, which tracks the integration of measurable quantities, and
sensitivity analysis, which assesses how model output is apportioned to
different sources of variation. The use of validation metrics for individual
measurements is extended to multiple measurements, with provisions for the
primacy hierarchy and sensitivity. This composite validation metric is
essential for quantitatively evaluating comparisons with experiments. To mount
successful and credible validation in magnetic fusion, a new culture of
validation is envisaged.
