The patient health questionnaire somatization-anxiety-depression scale: Validation of the PHQ-SAD in 4 clinical...

Somatization, anxiety, and depression are 3 highly comorbid conditions. Although validated scales exist for each SAD triad component, a composite measure could have complementary clinical and research utility. We examine validity of the Patient Health Questionnaire Somatic-Anxiety-Depression (PHQ-SAD) scale.

Baseline data from 4 clinical trials (2 in primary care, 1 in oncology, and 1 in the emergency department) totaling 1324 patients were analyzed. The PHQ-SAD comprises 25 items including the PHQ-8 for depression, the GAD-7 for anxiety, and 10 items from the PHQ-15 for somatic symptoms. The internal reliability, minimally important difference (MID), and factorial validity of the PHQ-SAD were examined.

Overlap of the 3 SAD symptoms across the 4 trials was substantial: the proportion with only 1 symptom of moderate severity ranged from 21 % to 43 %, whereas the proportion with moderate severity on all 3 symptoms ranged from 24 % to 46 %. The PHQ-SAD demonstrated high internal reliability (McDonald's omega of 0.88 to 0.95) in all 4 trials. PHQ-SAD scores can range from 0 to 65 (with higher scores indicating greater symptom severity), and cutpoints of 15, 30, and 45 represent mild, moderate and severe SAD symptom burden. Preliminary estimates from two distribution-based methods suggest 4 points as the PHQ-SAD minimally important difference (MID). Bi-factor analysis indicated sufficient unidimensionality of the PHQ-SAD score.

The PHQ-SAD is a reliable and factorially valid composite measure of somatic, anxiety and depressive symptoms which may be useful as a single measure for assessing SAD symptoms and for monitoring outcomes of transdiagnostic treatments. Trial Registration clinicaltrials.gov Identifier: NCT04811521 (PACER); NCT00926588 (SCOPE); NCT00313573 (INCPAD); NCT0175730 (CAMMPS).