Evaluation of the Brazilian version of Patient Health Questionnaire (PHQ-9) in Quilombola population using the Item Response Theory

Introduction. The Patient Health Questionnaire (PHQ-9) is one of the most validated tools used to detect depressive episodes in Brazil. Objective. This study investigates the psychometric properties of the PHQ-9 using the Item Response Theory. Method. We used the gradual response model to assess depression in 764 residents of Brazilian rural communities of descended from slaves (quilombos) from the county of Vitoria da Conquista, state of Bahia, Brazil, who had responded to PHQ-9. We estimated the parameters for item discrimination and difficulty. Results. The items of the PHQ-9 showed the ability to discriminate from moderate to very high. The items evaluating thoughts of hurting oneself and death showed the greatest discrimination while feeling depressed showed the lowest discrimination. Discussion and conclusion. The Item Response Theory enables advances in the analysis of the psychometric properties of the screening tools assessing depression, and indicates that PHQ-9 can be used in rural populations in Brazil.