Evidence for validity of the Swedish self-rated 36-item version of the World Health Organization Disability Assessment Schedule 2.0 (WHODAS 2.0) in patients with mental disorders: a multi-centre cross-sectional study using Rasch analysis

Journal of Patient-Reported Outcomes

Table 3 Recommended and observed values of validity criteria for the Swedish WHODAS 2.0, n = 780

Criterion	Recommended value	Domain 1	Domain 2	Domain 3	Domain 4	Domain 5	Domain 5a n = 780	Domain 5b n = 652	Domain 6	All domains
Unidimensionality (PCA of residuals)
Variance explained by measures	> 60%	55	54	45	51	66	77	76	57	48
Eigenvalue of the unexplained variance in 1^st contrast, logits	< 2.0	1.6	1.6	1.9	1.6	3.9	1.6	1.9	1.6	3.8
Disattenuated correlation	> 0.70	0.89	1	1	1	1	0.95	0.88	0.94	0.80
Reliability
Cronbach’s alpha	> 0.80	0.87	0.85	0.70	0.82	0.93	0.94	0.95	0.88	0.96
Person reliability	> 0.80	0.79	0.57	0.23	0.67	0.86	0.90	0.91	0.83	0.91
Item reliability	> 0.80	0.98	0.99	0.99	0.99	0.99	0.99	0.96	0.99	0.99
Person separation, logits	≥ 2	1.91	1.14	0.55	1.43	2.53	2.95	3.14	2.22	3.18
Item separation, logits	≥ 2	7.99	8.15	9.75	9.68	8.44	11.60	4.70	12.56	13.08
Targeting
Mean person ability, logits*	± 1	1.91	2.46	2.17	1.37	1.20	2.29	1.57	0.94	1.21
Ceiling effect	≤ 2%	11.5	31.5	37.2	14.6	12.8	19.7	19.3	4.6	2.7
Floor effect	≤ 2%	0	0.1	0	0	1.2	2.2	7.4	0	0
Effective operational range	≥ 90%	83	58	52	73	78	70	69	92	92

Deviations from the recommendation are in bold. *Reversed order of rating scale categories: low scores indicate greater difficulty
Domains: D1, Understanding and communicating; D2, Getting around; D3, Self-care; D4, Getting along with people; D5, Life activities; and D6, Participation in society. D5, Life activities, is divided in two areas: D5a = Domestic responsibilities, and D5b = Work and school. (PCA, principal component analysis.)