The selection of an appropriate outcome measure is crucial to the success of a clinical trial, in order to obtain accurate results, which, in turn, influence patient care and future research. Outcomes that can be directly measured are mortality/survival. More frequently, neurology clinical trials evaluate outcomes that cannot be directly measured, such as disability, cognitive function, or change in symptoms of the condition under study. These complex outcomes are abstract ideas or latent constructs and are measured using rating scales. Functional rating scales typically assess the ability of patients to perform tasks and roles for everyday life. Rating scales should be valid (measure what they are supposed to measure), reliable (provide similar results if administered under the same conditions), and responsive (able to detect clinically important changes over time). The clinical relevance of rating scales depends on their ability to detect a minimal clinically important difference, and should be distinguished from statistical significance. Most rating scales are ordinal scales and have limitations. Modern psychometric methods of Rasch analysis and item response theory, termed latent trait theory, are increasingly being utilized to convert ordinal data to interval measurements, both to validate existing scales and to develop new scales. Patient-reported outcomes are being increasingly used in clinical trials and have a role in clinical quality assessment. The PROMIS and NeuroQoL databases are excellent resources for rigorously developed and validated patient-reported outcomes.
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