The criterion for item convergent validity (item-scale correlations ≥ 0.40) was satisfied by all items in TREAT RLS 2. In TREAT RLS 1, all except two items met the criterion for item convergent validity.
Results of tests of item convergent validity, item discriminant validity, reliability, and floor and ceiling effects are presented in Table 4.
The RLSQoL was assessed for the following psychometric properties: item convergent validity (item-scale correlations of ≥ 0.4) [ 20], floor and ceiling effects (the percentage scoring the lowest and highest possible scores), internal consistency reliability (Cronbach's alpha ≥ 0.7), concurrent validity, known groups validity, clinical validity and responsiveness.
Both questionnaires showed sufficient item to item convergent validity and item discriminant validity.
To determine discriminant, divergent, and convergent validity, items of the EDY-Q were correlated with items of the ChEDE-Q using Spearman's Rank correlation coefficient.
Hence, in order to demonstrate convergent validity, items that measure the same construct (i.e. a trait) should be highly correlated with one another [ 25].
Multi-trait analysis was used to assess construct validity, including item convergent validity and item discriminant validity [ 17].
Multi-trait analyses were used to assess construct validity, including item convergent validity and item discriminant validity.
This included a Multitrait Analysis (MA) that evaluated the final structure of the questionnaire by describing item convergent validity and item discriminant validity [ 29].
Together, the item convergent validity and item discriminant validity results demonstrated the satisfactory validity of the QUALIOST® hypothesised structure for each language version tested (7 countries) and for overall data (11 countries) (see Table 1).
