Translating measurement into practice: Brazilian norms for depressive symptom assessment with the Patient Health Questionnaire (PHQ-9)

Objectives: To provide practical norms for measuring depressive symptoms with the Patient Health Questionnaire 9 (PHQ-9) in Brazil through a state-of-the-art psychometrics analysis.Methods: We used a large representative dataset from the 2019 Brazilian National Health Survey (Pesquisa Nacional de Saude - 2019), which included 90,846 Brazilian citizens. To assess scale structure, we assessed a unidimensional model using confirmatory factor analysis. Item response theory was used to characterize the distribution of depressive symptoms. Summed- and mean-based PHQ-9 scores were then linked using item response theory-based scores in generalized additive models. Finally, percentiles, T scores, and a newly developed score, called the decimal score (D score), were generated to describe PHQ-9 norms for the Brazilian population.Results: C onfirmatory factor analysis revealed a good fit to the unidimensional model, being invariant to age and sex. Item response theory captured item-level information about the latent trait (reliable from 1 to 3 SDs above the mean). Brazilian norms were presented using summed scores, T scores, and D scores.Conclusion: This is the first study to determine Brazilian 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.