Table 2.

Psychometric measures considered in patient-reported outcomes instrument evaluations.

Measure	Definition	Common methods of assessment	Interpretationa
Validity (degree to which an instrument measures the concept it is intended to measure)28,30,31,59
Content validity	Extent to which the instrument includes the most relevant and important aspects of a concept54	Stakeholder focus groups, interviews, surveys	Qualitative evidence from development and pre-testing60
Construct validityb	Evidence that relationships among items, domains, and concepts conform to a priori hypotheses28	Correlation statistics	≥0.70 supports strong correlation
Congruent	Extent to which measure correlates with measure assessing the same construct
Known group	Extent to which measure is sensitive to differences and similarities in groups with known attributes
Responsiveness	Extent to which instrument can detect changes in the construct being measured over time30	Score change statistics	Statistically significant difference in scores pre- and post-clinically relevant events29
Reliability (degree to which an instrument is free from measurement error)30, 31,59
Internal consistency reliability	Degree of the interrelatedness among the items in a multi-item measure30,31	Cronbach’s α	≥0.70: adequate internal consistency60
Test-retest reliability	Measure of the ability to provide consistent scores over time in a stable population30	Intraclass correlation coefficient; Kappa statistic	≥0.70: supports test-retest reliability29

^aInterpretation score thresholds are not well established and may differ across populations and sources.

^bConstruct validity was considered as congruent and known group validity as these were the construct validity sub-types most commonly assessed in identified instruments.