Table 8.
Adapted from Table 4 of the FDA guidelines for measurement properties reviewed for PRO instruments used in clinical trials
| 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 |
aReported in Wild et al. 2009 [10]; bFurther additional information available from the authors.
✓=tested; x=not tested.
ACTS Anti-Clot Treatment Scale, FDA US Food and Drug Administration, NA not applicable, PRO patient-reported outcome.