Original Research

Confirmatory factor analysis of the Patient Health Questionnaire-9: A study amongst tuberculosis patients in the Free State province

Gladys Kigozi
Southern African Journal of Infectious Diseases | Vol 35, No 1 | a242 | DOI: https://doi.org/10.4102/sajid.v35i1.242 | © 2020 Gladys Kigozi | This work is licensed under CC Attribution 4.0
Submitted: 27 August 2020 | Published: 21 December 2020

About the author(s)

Gladys Kigozi, Department Center for Health Systems Research & Development, Faculty Humanities, Free State University, Bloemfontein, South Africa


Background: There is growing evidence that depression is frequently comorbid with tuberculosis (TB) and is often associated with a decreased quality of life and poor treatment outcomes. The Patient Health Questionnaire (PHQ-9) is widely used to screen for depression in clinical settings in low-and middle-income countries. This study examined the construct validity and reliability of an interviewer-administered PHQ-9 in a sample of new TB patients in the Free State province of South Africa.

Methods: A pilot study was conducted in 2019 amongst 208 new adult TB patients attending primary healthcare facilities in the Lejweleputswa District in the Free State. Trained fieldworkers administered a structured questionnaire comprising of questions on patient’s socio-demographic characteristics and the nine-item PHQ-9 to the patients. Confirmatory factor analysis and Cronbach’s alpha were respectively used to investigate the construct validity and internal consistency of the PHQ-9.

Results: The model was a good fit, with a Tucker–Lewis index of 0.976, a comparative fit index of 0.982 and a root mean square error of approximation of 0.062 (90% CI: 0.032–0.089). All indicators showed significant positive factor loadings, with standardised coefficients ranging from 0.467 to 0.799. The PHQ-9 was characterised by a single factor latent structure – depression – underlying all items. The Cronbach’s alpha of the scale was 0.84.

Conclusion: The results support a unidimensional structure of the PHQ-9, with satisfactory internal consistency implying that the scale is valid and reliable. The TB programme can confidently consider the PHQ-9 for the routine assessment of depression amongst TB patients in the Free State province and similar settings.


tuberculosis; depression; PHQ-9; construct validity; confirmatory factor analysis.


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Crossref Citations

1. Construct validity and reliability of the generalised anxiety disorder-7 scale in a sample of tuberculosis patients in the Free State Province, South Africa
Gladys Kigozi
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doi: 10.4102/sajid.v36i1.298