Differential Item Functioning of WHOQOL-BREF in nine Iberoamerican countries

WHOQOL-BREF measures the individual's perception on their personal situation in contrast to their expectations, goals, standards and concerns. Previous results did not support the original factor structure in a sample of 9 Iberoamerican countries. However, Differential Item Functioning (DIF) has yet to be thoroughly addressed in these populations. Therefore, the main purpose of this study was to analyze DIF in Iberoamerican countries. WHOQOL-BREF was administered to a sample of 1972 individuals from nine Spanish-speaking countries and ages between 17 and 34 years (mean = 21.21, SD = 3.40, 62.5% women). In order to assess the DIF, each item was modeled through a proportional odds logistic regression with nationality in the linear predictor. All models were statistically non-equivalent to the null models and the proportion of correct classification of the models ranging from 0.336 to 0.473, which leads us to conclude that the nationality of the participants plays a relevant role on the response in the items of WHOQOL-BREF. In spite of a common language, differences in cultural, historical, and social variables across these nine countries could be influencing the individual's perception of quality of life. In order to minimize those differences, specific adaptations of the Spanish-version of WHOQOL-BREF for each country should be considered.