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Table 1 Adapted from table 4 of the FDA draft guidelines for measurement properties reviewed for PRO instruments used in clinical trials

From: The Cervical Dystonia Impact Profile (CDIP-58): Can a Rasch developed patient reported outcome measure satisfy traditional psychometric criteria?

Measurement Property Test Methods used in testing the CDIP-58
Reliability Test-retest
Internal consistency Whether the items in a domain are intercorrelated, as evidenced by an internal consistency statistic (e.g., coefficient alpha)
Inter-interviewer reproducibility (for interviewer-administered PROs only) Agreement between responses when the PRO is administered by two or more different interviewers NA
Validity Content-related *
Ability to measure the concept (also known as construct-related validity; can include tests for discriminant, convergent, and known-groups validity) Whether relationships among items, domains, and concepts conform to what is predicted by the conceptual framework for the PRO instrument itself and its validation hypotheses.
Ability to predict future outcomes (also known as predictive validity) Whether future events or status can be predicted by changes in the PRO scores
Ability to detect change Includes calculations of effect size and standard error of measurement among others **
Interpretability Smallest difference that is considered clinically important; this can be a specified difference (the minimum important difference (MID)) or, in some cases, any detectable difference. The MID is used as a benchmark to interpret mean score differences between treatment arms in a clinical trial /✗***
Responder definition – used to identify responders in clinical trials for analyzing differences in the proportion of responders between treatment arms Change in score that would be clear evidence that an individual patient experienced a treatment benefit. Can be based on experience with the measure using a distribution-based approach, a clinical or non-clinical anchor, an empirical rule, or a combination of approaches. NA
  1. = tested; ✗ = not tested; * Reported in Cano et al 2004 [6]; ** Reported in Cano et al 2006 [28]; *** Although not including MID in our responsiveness paper (Cano et al, 2006 [28]), we include a comparison of relative responsiveness to existing PROs used in CD research in order to increase the interpretability of CDIP-58 change scores against these measures.