COSMIN definitions of measurement properties
| Measurement property | Definition |
| Content validity | The degree to which a PROM measures the construct(s) it purports to measure |
| Structural validity | The degree to which the scores of a PROM are an adequate reflection of the dimensionality of the construct to be measured |
| Internal consistency | The degree of inter-relatedness among the items |
| Cross-cultural validity | The degree to which the performance of the items on a translated or culturally adapted PROM are an adequate reflection of the performance of the items of the original version of the PROM |
| Measurement invariance | The proportion of the total variance in the measurements which is due to ‘true’ differences between patients |
| Reliability | The degree to which the measurement is free from measurement error |
| Reliability (extended definition) | The extent to which scores for patients who have not changed are the same for repeated measurement under several conditions: eg, using different sets of items for the same PROM (internal consistency); over time (test–retest); by different persons on the same occasion (inter-rater); or by the same persons (ie, raters or responders) on different occasions (intra-rater) |
| 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 |
| Construct validity | The degree to which the scores of a PROM are consistent with hypotheses (for instance with regard to internal relationships, relationships to scores of other instruments or differences between relevant groups) based on the assumption that the PROM validly measures the construct to be measured |
| Responsiveness | The ability of a PROM to detect change over time in the construct to be measured |
COSMIN, Consensus-based Standards for the selection of health Measurement Instruments; PROM, patient-reported outcome measure.