Psychometric evaluation of the patient health questionnaire-9 in helping professionals: factor structure, gender invariance, and construct validity

Helping professionals are at elevated risk of depression due to the emotional demands of their work, yet the PHQ-9 has not been psychometrically validated in this population in Central Europe. This study examines the factorial structure, measurement invariance, and construct validity of the Patient Health Questionnaire-9 (PHQ-9) in a sample of 2,893 Slovak helping professionals. Confirmatory factor analysis was used to compare one-factor, two-factor, four-factor, and bifactor models. All models demonstrated acceptable to excellent fit. The four-factor model provided the most differentiated structure among the correlated models, while the bifactor analysis revealed essential unidimensionality. Measurement invariance across gender was established at configural, metric, scalar, and strict levels for all correlated factor models. Construct validity was supported through significant associations with anxiety, self-criticism, self-reassurance, compassion fatigue, compassion satisfaction, and burnout. The one-factor model consistently showed the strongest or comparable associations with external constructs, with only marginal differences between factors and largely overlapping confidence intervals. These findings establish the PHQ-9 as a psychometrically sound instrument for assessing depression in helping professionals, with the total score suitable for both screening and construct validity assessment.