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.