Measuring what matters: does 'objectivity' mean good science?

Purpose. While the limitations of self-report measures are clearly acknowledged, less apparent is attention to the potential limitations of their 'objective' counterparts leading to the assumption that objectivity results in more robust and scientifically valid measurement tools. This article aims to: (1) test this assumption; (2) consider the implications of advocating for a measure on the basis of its objectivity; (3) propose an alternative approach to measure selection. Key findings and implications. A critical evaluation of one 'objective' measure highlights a number of potential limitations suggesting that the apparent willingness to adopt 'objective' measures with little questioning may be misguided. The possible implications of this are discussed and include a risk to the advancement of, and capacity for, knowledge in rehabilitation; or worse, of making clinical decisions based on erroneous conclusions. Conclusions. Characterising a measure on the basis of objectivity (or not) assumes an overly simplistic dichotomy that is unhelpful and perhaps misleading. We argue that assessing whether a measure is fit for purpose and makes mathematical sense is the key consideration. Indeed, in some cases, using both an 'objective' measure and a subjective rating scale may be appropriate and the only way of truly capturing the phenomenon of interest.