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The content validity of the items is supported by their close relation to established criteria and by the authors' clinical expertise in the field.
The choice of items is supported by the literature: Cheung and colleagues compared aggressive and non-aggressive schizophrenia patients (aggression assessed by the Staff Observation Aggression Scale) with respect to single items of the PANSS (Cheung et al, 1997).
The third item is supported by empirical evidence: our data suggest that the travel-times cost t for a single trip has also predominantly an exponential probability density within the range (4 leq t leq60) minutes (see Figure 4 left)) p t) approxlangle t rangle^{-1} expbigl -t/langle t ranglexpbigl -t/langle
WHODAS II: World Health Organization Disability Assessment Schedule II, ODI: Oswestry Disability Index, RDQ: Roland Morris Low Back Pain Disability Questionnaire, NHP: Nottingham Health Profile, SE: Standard Error The unidimensionality of the item bank was supported by the individual t-test showing 7.5% of tests as significant (CI 4.9%–10.2%).
The phase 2 PCA, with a revised pool of 48 items, indicated that four rather than five domains presented the best model giving rise to the 34-item PTOPS, which was supported by factor analyses conducted with phase 2 and phase 3 data which confirmed the independence of the domains providing evidence for the internal validity of the PTOPS scores.
Thus, factor analysis was applied to each domain separately to evaluate whether the assumption of a unique factor satisfactorily summarizing the items in each domain was supported by the data.
Aggregation of the individual PROFAD items into facet scores was supported by reliability analyses, which showed each of the facets to be highly consistent internally (range of Cronbach's alpha values: 0.74 to 0.97).
The homogeneity of item content for the SIQ/SIQ-JR was supported by good item-total correlations, with all correlations higher than 0.5 and median item-total correlations higher than 0.7 in the overall, male, and female samples.
Construct validity was supported by item-total correlations where all items in the symptom scale were sufficiently correlated (≥0.3).
