Translating measurement into practice: Brazilian norms for the Patient Health Questionnaire (PHQ-9) for assessing depressive symptoms.

Abstract

To provide practical norms for measuring depressive symptoms using the Patient Health Questionnaire 9 (PHQ-9) in Brazil using a state-of-art psychometrics analysis. We used a large and representative Brazilian dataset from the 'Pesquisa Nacional de Saúde - 2019'(PNS-2019), which includes 90,846 Brazilian citizens. First, to assess the scale structure, we assessed the unidimensional model using Confirmatory Factor Analysis (CFA). Second, we used Item Response Theory (IRT) to characterize depressive symptoms´ distribution. Then, we linked summed- and meanbased PHQ-9 scores with the IRT-based score by using generalized additive models. Finally, we generated percentiles, T scores, and a newly developed score, called D scores (decimal scores), to describe the PHQ-9 norms for Brazilian population. CFA revealed a good fit to the unidimensional model, showing to be invariant to age and sex. IRT captured item-level information of the latent trait (reliable from 1 to 3 standard deviations above the mean). Brazilian norms were presented using summed-, T-scores, and D-scores. This is the first study to define Brazilian´s norms for the PHQ-9 among a large representative sample, using robust psychometric tools. More precise PHQ-9 scores are now available and may be widely used in primary and specialized clinical care settings.