What do the PHQ-9, the GAD-7 and their variants miss in assessing young people presenting to youth mental health services?

Brief self-report measures offer significant benefits in youth mental health services by providing quick, efficient, and accessible assessment of mental health status. In this study, we describe the psychometric features of the Patient Health Questionnaire-9 (PHQ-9), the Generalised Anxiety Disorder-7 (GAD-7) and their shorter variants in 1063 young people at their first appointment to headspace youth primary care mental health services. Specific aims were to: (i) document the internal consistency, dimensionality, and measurement invariance for sex and age (12-14, 15-17, 18-21, 22-25 years) for the PHQ-9 and GAD-7; (ii) compare the full and shorter variants of the measures; and (iii) determine construct validity by correlating variants with measures of psychological distress, rumination, functioning, and quality of life. Two-factor models, comprising cognitive-affective and somatic symptom domains, best represented the dimensionality of both the PHQ-9 and GAD-7; measurement invariance for these models was found for sex and age-group. The PHQ-2, GAD-2, and PHQ-4 correlated strongly with the full versions of these measures and had strong internal consistency. Construct validity was noted for all variants of the PHQ-9 and GAD-7. As young people can present with high rates of somatic symptoms, we encourage clinicians and researchers to use subscale in addition to total scores for the PHQ-9 and GAD-7. We also caution the use of the shorter variants of these scales given they do not include somatic symptom items.