Sensitivity to change and minimal clinically important difference of the 7-item Generalized Anxiety Disorder Questionnaire (GAD-7)

Abstract

Background: Effective treatment requires regular follow-up and monitoring of symptoms. We investigated sensitivity to change and minimal clinically important difference of the Generalized Anxiety Disorder Scale (GAD-7).

Methods: This study included all participants from a multisite trial of chronic depression. Baseline and follow-up (12 and 48 weeks) data were used to assess treatment response. Effect sizes (ES) and standardized response means (SRM) of pre- and post-GAD-7 mean changes were calculated for subgroups of patients, who did or did not improve according to ratings in the Hamilton Rating Scale for Depression (HRSD-24).

Results: N = 261 patients were included in the analyses. In the subgroup of patients who improved according to HRSD-24, GAD-7 scores were significantly lower after 12 weeks (t = -6.31, df = 120, p < .001; ES = -0.51, SRM = -0.57), and 48 weeks of treatment (t = -12.68, df = 141, p < .001; ES = -1.0, SRM = -1.7), when compared to admission. In the group who worsened, GAD-7 scores were significantly higher after 12 weeks (t = 2.96, df = 41, p = .005; ES = 0.30, SRM = 0.46), and increased after 48 weeks (t = 1.99, df = 21, p = .059; ES = 0.37, SRM = 0.43), when compared to baseline. The unchanged group showed no significant difference between baseline and follow-up. MCID was estimated 4 points on the GAD-7 total score.

Limitations: Confirmation of these findings and further investigation of the GAD-7 in populations and trials focusing on anxiety-specific treatment is highly recommended.

Conclusions: Results show that the GAD-7 is sensitive to detect change in psychopathology over the course of treatment.

Keywords: Anxiety; Minimal clinically important difference; Psychometrics; Responsiveness; Sensitivity to change.