Validation of clinical prediction models: what does the “calibration slope” really measure?

Background and ObjectivesDefinitions of calibration, an aspect of model validation, have evolved over time. We examine use and interpretation of the statistic currently referred to as the calibration slope.MethodsThe history of the term “calibration slope”, and usage in papers published in 2016 and 2017, were reviewed. The behaviour of the slope in illustrative hypothetical examples and in two examples in the clinical literature was...