Stefan Cano, Stefan Cano, Hobart

In this review we discuss health measurement with a focus on psychometric methods and methodology. In particular, we examine some of the key issues currently facing the use of clinician and patient rating scales to measure the health outcomes of disease and treatment. We present three key facts and flag one crucial problem. First, the numbers generated by scales are increasingly used as the measurements of the central dependent variables upon which clinical decisions are frequently made. The rising profile of rating scales has significant implications for scale construction, evaluation, and selection, as well as for interpreting studies. Second, rating scale science is well established. Therefore, it is important to learn the lessons from those who have built and established the science over the last century. Finally, the goal of a rating scale is to measure. As such, over the last half century, developments in rating scale (psychometric) methods have caused a refocus in the way we should be measuring health. In particular, newer methods have significant clinical advantages over traditional approaches. These should be seriously considered for inclusion in everyday practice. This leads us to the central problem with health measurement, which is that we cannot currently be sure what most rating scales are measuring. This is because the methods we have in place to ensure the validity of rating scales fall short of what is actually required. We expand on this point, and provide some potential routes forward to help address this important problem.