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 |