Table 3.
Definition of Measurement Properties
| Measurement Property | Definitiona |
|---|---|
| Reliability | |
| 1. Internal consistency | The degree/extent to which items in a (sub)scale are inter‐correlated, thus measuring the same construct |
| 2. Reliability | The proportion of the total variance in the measurements due to true differences among patients |
| 3. Measurement error | The systematic and random error of a patient's score that is not attributed to true changes in the construct to be measured |
| Validity | |
| 4. Content validity | The degree to which the content of an instrument is an adequate reflection of the construct to be measured |
| 5. Structural validity | The degree to which the scores of an instrument are an adequate reflection of the dimensionality of the construct to be measured |
| 6. Construct validity (hypothesis testing) | The degree to which the scores of an instrument are consistent with hypotheses (eg, with regard to internal relationships, relationships to scores of other instruments, or differences between relevant groups) based on the assumption that the other instrument validly measures the construct |
| 7. Criterion validityb | The extent to which scores on a particular questionnaire relate to a gold standard |
| 8. Cross‐cultural validity | The degree to which the performance of the items on a translated or culturally adapted health‐related patient reported outcomes (HR‐PRO) instrument are an adequate reflection of the performance of the items of the original version of the HR‐PRO instrument |
| Responsiveness | |
| 9. Responsiveness | The ability of an instrument to detect change over time in the construct to be measured |