Table 1 COSMIN definitions of domains, measurement properties and aspects of measurement properties [7]

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: e.g., using different sets of items from the same OMI (internal consistency); over time (test-retest); by different persons on the same occasion (inter-rater); or by the same persons on different occasions (intra-rater)

Internal consistency

The degree of interrelatedness among the items

Reliability

The proportion of the total variance in the measurements which is due to ‘true’ differences between patients

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

The degree to which an OMI measures the construct(s) it purports to measure

Content validity

The degree to which the content of an OMI is an adequate reflection of the construct to be measured

Face validity

The degree to which (the items of) an OMI indeed seems to be an adequate reflection of the construct to be measured

Construct validity

The degree to which the scores of an OMI are consistent with hypotheses (e.g., with regard to internal relationships, relationships to scores of other OMIs, or differences between relevant groups) based on the assumption that the OMI validly measures the construct to be measured

Structural validity

The degree to which the scores of an OMI are an adequate reflection of the dimensionality of the construct to be measured

Hypotheses testing

Idem construct validity

Cross-cultural validity

The degree to which the performance of the items on a translated or culturally adapted OMI are an adequate reflection of the performance of the items of the original version of the OMI

Criterion validity

The degree to which the scores of an OMI are an adequate reflection of a gold standard

Responsiveness

The ability of an OMI to detect change over time in the construct to be measured

Responsiveness

Idem responsiveness

Interpretability^a

The degree to which one can assign qualitative meaning (i.e., clinical or commonly understood connotations) to an OMI’s quantitative scores or change in scores