Table 4.

Terwee et al. quality for health status questionnaires

1. Content validity	The extent to which the concepts of interest are comprehensively represented by the items in the questionnaire
2. Internal consistency	The extent to which items in a (sub)scale are inter-correlated, thus measuring the same construct
3. Criterion validity	The extent to which scores on a particular questionnaire relate to a gold standard
4. Construct validity	The extent to which scores on a particular questionnaire relate to other measures in a manner that is consistent with theoretically derived hypothesis concerning the concepts that are being measured.
5. Reproducibility	a. Agreement The extent to which the scores on repeated measures are close to each other (absolute measurement error) b. Reliability The extent to which patients can be distinguished from another, despite measurement errors (relative measurement error)
6. Responsiveness	The ability of a questionnaire to detect clinically important changes over time.
7. Floor and ceiling effects	The number of respondents who achieved the lowest or highest possible score.
8. Interpretability	The degree to which one can assign qualitative meaning to quantitative scores.