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Table 8 Adapted from Table 4 of the FDA guidelines for measurement properties reviewed for PRO instruments used in clinical trials

From: The Anti-Clot Treatment Scale (ACTS) in clinical trials: cross-cultural validation in venous thromboembolism patients

Measurement property Test Methods used in testing the ACTS
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 a
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 x
Ability to detect change Includes calculations of effect size and standard error of measurement among others
Interpretability Smallest difference that is considered to be clinically important; this can be a specified difference (the minimum important difference) or, in some cases, any detectable difference. The minimum important difference is used as a benchmark to interpret mean score differences between treatment arms in a clinical trial b
Responder definition – used to identify responders in clinical trials for analysing 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. aReported in Wild et al. 2009 [10]; bFurther additional information available from the authors.
  2. =tested; x=not tested.
  3. ACTS Anti-Clot Treatment Scale, FDA US Food and Drug Administration, NA not applicable, PRO patient-reported outcome.