Disease Activity Measures in Paediatric Rheumatic Diseases

Table 2

Definitions of domains of measurement properties, adapted from COSMIN taxonomy [28].

Domain	Measurement property	Definition
Reliability	Internal consistency	The degree of interrelatedness among items
	Reliability	The proportion of the total variance in measurements which is due to “true” differences among patients
	Measurement error	The systematic and random errors of a patient’s score that is not attributed to true changes in the construct being measured
Validity	Content validity	The degree to which the content of an instrument is an adequate reflection of the construct to be measured
	Face validity	The degree to which the items look to be an adequate reflection of the construct to be measured
	Construct validity	The degree to which the scores of an instrument are consistent with hypotheses (e.g., relationships to scores of other instruments) based on the assumption that the instrument validly measures the construct to be measured
	Criterion validity	The degree to which the scores of an instrument are an adequate reflection of a “gold standard”
Responsiveness		The ability of an instrument to detect change over time in the construct to be measured
Interpretability		The degree to which one can assign qualitative meaning to an instrument’s quantitative scores or change in scores