Validity of the Patient Health Questionnaire Anxiety and Depression Scale (PHQ-ADS) in Patients With Dizziness

HYPOTHESIS: The Patient Health Questionnaire Anxiety and Depression Scale (PHQ-ADS) will be a valid and reliable combined measure of depression and anxiety in people with vertigo and dizziness. BACKGROUND: Co-occurrence of depressive, anxiety, and somatic symptoms are common. The Patient Health Questionnaire-9 (PHQ-9) and Generalized Anxiety Disorder Scale-7 (GAD-7) measure symptoms of depression and anxiety respectively, although measuring them separately may be suboptimal in people who have illness-related distress. There is some evidence that these scales can be combined in long-term conditions resulting in the PHQ-ADS, but validity is yet to be determined in people with vertigo and dizziness. METHODS: Two separate datasets from a tertiary vestibular clinic were analyzed where the PHQ-ADS was completed at initial clinical assessment (n = 624) and while on a waiting list (n = 185). A cross-sectional design was used to examine the factor structure (confirmatory factor analysis), internal consistency (omega index), and construct validity (Pearson correlation coefficient) of the PHQ-ADS. Construct validity was determined against the dizziness handicap inventory (DHI). RESULTS: A bi-factor PHQ-ADS model had good fit to the data (χ2 = 397.163, 249.763; comparative fit index [CFI] = 0.954, 0.919; Tucker-Lewis index [TLI] = 0.938, 0.892; root mean squared error of approximation [RMSEA] = 0.076, 0.098). The general distress factor explained 81 to 85% of the common variance between items. There were moderate to large significant positive correlations between the PHQ-ADS and DHI. CONCLUSION: The PHQ-ADS appears to have good structural validity in patients with vertigo and dizziness. Clinicians and researchers can use this scale where a composite psychological measure is desired.