Term	Definition
Content validity	The degree to which the content of an outcome measure is an adequate reflection of the construct to be measured
Structural validity	The degree to which the scores of an outcome measure are an adequate reflection of the dimensionality of the construct to be measured
Internal consistency	The degree of the interrelatedness among the items
Measurement invariance	The degree to which respondents from different groups with the same latent trait level respond similarly to a particular item
Reliability	The extent to which scores for patients who have not changed are the same for repeated measurement under several conditions: for example, over time (test–retest) or by different persons on the same occasion (inter‐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
Hypothesis testing for construct validity	The degree to which the scores of an outcome measure are consistent with hypotheses based on the assumption that the outcome measure validly measures the construct to be measured
Responsiveness	The ability of an outcome measure to detect change over time in the construct to be measured