Value added? A pragmatic analysis of the routine use of PHQ-9 and GAD-7 scales in primary care

Background: Depression and anxiety are common and often co-occur. The PHQ-9 and GAD-7 scales are frequently used to measure symptoms and track treatment response in these conditions. These instruments show substantial correlation. This study investigates the similarity between concurrent pairs of PHQ-9 and GAD-7 when used to monitor treatment outcomes.Methods: Data originated from a clinical registry within a behavioral health collaborative care program for a large primary care network. A total of 31,974 pairs of PHQ-9 and GAD-7 scores, from 5402 patient care episodes, were analyzed for correlation coefficient, distribution of score differences, and overlap in symptom burden categories. A Number Needed to Identify was calculated to quantify the marginal effect of performing both scales.Results: The correlation coefficient (Spearman's rho) was 0.74. 78.4% of concurrent scores were within 4 points of each other, and 56.4% of score pairs fell into the same severity class. The Number Needed to Identify for PHQ-9 was 8 while the NNI for GAD-7 was 14.1.Conclusions: Concurrent pairs of PHQ-9 and GAD-7 were strongly associated and often similar in severity. In terms of identifying clinically significant symptoms, the marginal effect of using both measures appears moderate.