Table 1 Explanations of key psychometric concepts described in this paper
Explanatory factor analysis | Statistical exploration of the underlying number of factors included in a questionnaire. The factor structure is the described by the number of factors, the items’ loading and the overall explained variance |
Confirmatory factor analysis | Statistical analysis testing whether the data fit a hypothesized measurement model of the questionnaire. Indicators of adequate model fit are given in the text. |
Feasibility | Indicates whether test persons find the questionnaire easy or complicated to complete. |
Internal consistency | Describes how well subscale items of the questionnaire go together, and eventually subscales in relation to the total questionnaire. |
Criterion validity | The questionnaire’s correlation with ‘gold standard’ questionnaires for the same concepts. |
Convergent validity | High correlations with other questionnaires covering the same concepts. |
Divergent validity | Low correlations with questionnaires covering other concepts. |
Construct validity | How well the questionnaire corresponds to other ways of measuring the construct i.e. various adverse effects. |
Predictive validity | The ability of the questionnaire score to predict important future outcome. |
Responsiveness to change | The ability of the questionnaire to identify clinical changes in the domains covered by the questionnaire. |