Abstract
Adequate measurement is an essential component of the assessment of mental
health disorders and symptoms such as depression and anxiety. The present study
investigated sex-specific differences in the Patient Health Questionnaire-9 (PHQ-9) and
Generalized Anxiety Disorder-7 (GAD-7). This comprehensive cross-sectional design
study pursued four objectives: measurement invariance of PHQ-9 and GAD-7 between
male and female; depression and anxiety prevalence differences; cross-sex differences
in the relationship between depression and anxiety; and a comparison of symptom
heterogeneity. A sample of 1966 (male D 592; female D 1374; mean age D 21 years)
students from South Africa completed the PHQ-9 and the GAD-7. Data analyses for
measurement invariance, latent class analysis, inter-variable correlations and group
comparisons were conducted in Mplus. The two-dimensional PHQ-9 achieved scalar
invariance, while the GAD-7 yielded metric invariance. The somatic and non-somatic
latent dimensions of depression were compared and showed no significant difference
between male and female groups. The positive relationship between depression and
anxiety was also not significantly different between the two groups. While the PHQ-9
symptoms formed three classes in the male group, and four classes in the female group,
the GAD-7 had the same number of classes (three) and a similar pattern between the
two groups. These findings hold implications for the measurement, assessment and
understanding of symptom manifestation and distribution, as well as the treatment of
depression and anxiety in South Africa.