Table 1.

Definitions of psychometric measurement properties (adapted from the COSMIN taxonomy^{( 31 )})

Term	Definition
Content validity	The ability of a questionnaire to adequately cover all relevant topics of the construct (concept) to be measured
Face validity	The degree to which the items of a questionnaire appear (on ‘face value’) as though they are an adequate reflection of the construct (concept) to be measured. Considered to be an aspect of content validity
Construct validity	The degree to which the scores on a questionnaire are consistent with hypotheses (e.g. with regard to differences between relevant groups) based on the assumption that the questionnaire validly measures the construct to be measured
Internal reliability	The degree of the interrelatedness among the items of a questionnaire; also referred to as internal consistency or homogeneity
Temporal stability	The ability of a questionnaire to detect change over time in the construct to be measured; also referred to external reliability
Responsiveness	The ability of a questionnaire instrument to detect change over time in the construct to be measured
Dimensionality*	The extent to which the items measure a hypothesized concept distinctly. In unidimensional scales, all items are said to reflect a single construct; in multidimensional scales, several topics (sub-sections) of the same construct are being measured
Criterion validity	The degree to which the scores of a questionnaire are an adequate reflection of a ‘gold standard’

COSMIN, COnsensus-based Standards for the selection of health Measurement Instruments.

^*This definition was not derived from COSMIN. In Classical Test Theory, dimensionality is determined by performing factor analysis.