Table I.

Definitions of the measurement properties.

	Definitions of the measurement properties
Internal consistency	The degree of the interrelatedness among the items
	“Do the different questions in a PROM that are meant to measure the same general construct produce similar scores?”
Reliability	The proportion of the total variance in the measurements which is because of “true” differences among patients
	“How close are repeated measurements?”
Measurement error	The systematic error and random error of a patient’s score that are not attributed to true changes in the construct to be measured
	“What amount of change in a score cannot be considered a real or true change?”
Content validity	The degree to which the content of a health-related patient-reported outcomes (HR-PRO) instrument is an adequate reflection of the construct to be measured
	“Are all items relevant for the specific population and have important activities been missed?”
Structural validity	The degree to which the scores of an HR-PRO instrument are an adequate reflection of the dimensionality of the construct to be measured
	“Do all items in a PROM reflect single or multiple constructs?”
Hypotheses testing	The degree to which the scores of an HR-PRO instrument 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 HR-PRO instrument validly measures the construct to be measured
	“What is the expected relationship with other PROMs assessing comparable constructs?”
Cross-cultural validity	The degree to which the performance of the items on a translated or culturally adapted HR-PRO instrument is an adequate reflection of the performance of the items of the original version of the HR-PRO instrument
	“Has the PROM been correctly translated and retested in another language and cultural setting?”
Criterion validity	The degree to which the scores of an HR-PRO instrument are an adequate reflection of a “gold standard”
	“Is the PROM tested against the benchmark PROM?”
Responsiveness	The ability of an HR-PRO instrument to detect change over time in the construct to be measured
	“If patients improve or worsen over time does this change in the PROM accordingly?”
Interpretability*	The degree to which one can assign qualitative meaning—that is, clinical or commonly understood connotations—to an instrument’s quantitative scores or change in scores
	“What do the scores or change in scores of a PROM mean?”

Clarification in bold

^*Is not a real measurement property, but nevertheless it is a meaningful requirement for the applicability of PROMs in research

PROM, patient-reported outcome measure