The World Health Organization Quality of Life instrument for people with intellectual and physical disabilities (WHOQOL-Dis): evidence of validity of the Brazilian version

Background: The number of people with disabilities in Brazil and worldwide has grown substantially in recent decades. Cross-cultural quality of life instruments can be helpful in the development of interventions designed to meet the needs of this population and contribute to rational allocation of resources. This study sought to provide evidence of validity and reliability the Brazilian Portuguese version of WHOQOL-Dis-D (a cross-cultural, multicentre instrument developed by the WHOQOL-Group for the assessment of quality of life in persons with physical disability - PD) and WHOQOL-Dis-ID (for persons with intellectual disability - ID). Methods: Classical psychometric methods were used to conduct independent analyses of the PD and ID samples. Criterion groups were established for analysis of construct validity. Concurrent validity was assessed in relation to SWLS and BDI-II scores; discriminant validity, in relation to WHODAS-II. Cronbach alpha was used to test the instrument scales and subscales for reliability. The ID subgroup was retested, and test-retest reliability assessed by means of intraclass correlation coefficients and paired Student's t-test. Results: A total of 162 (98 females) people with PD and 156 (55 females) people with ID participated in the study. Cronbach alpha was satisfactory across practically all domains and factors in the PD subsample. In IDs, most factors or domains had coefficients higher than 0.70, but four subscales exhibited less satisfactory performance. Evidence of construct and concurrent validity and reliability were obtained. Conclusions: The analyses presented herein provide satisfactory evidence of the validity and reliability of the instrument and corroborated the factor structure revealed during cross-cultural research. Further studies with larger sample sizes are required to obtain additional evidence of validity and reliability.