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

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

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.