How much change is enough? Evidence from a longitudinal study on depression in UK primary care

Background The Patient Health Questionnaire (PHQ-9), the Beck Depression Inventory (BDI-II) and the Generalised Anxiety Disorder Assessment (GAD-7) are widely used in the evaluation of interventions for depression and anxiety. The smallest reduction in depressive symptoms that matter to patients is known as the Minimum Clinically Important Difference (MCID). Little empirical study of the MCID for these scales exists. Methods A prospective cohort of 400 patients in UK primary care were interviewed on four occasions, 2 weeks apart. At each time point, participants completed all three questionnaires and a 'global rating of change' scale (GRS). MCID estimation relied on estimated changes in symptoms according to reported improvement on the GRS scale, stratified by baseline severity on the Clinical Interview Schedule (CIS-R). Results For moderate baseline severity, those who reported improvement on the GRS had a reduction of 21% (95% confidence interval (CI) -26.7 to -14.9) on the PHQ-9; 23% (95% CI -27.8 to -18.0) on the BDI-II and 26.8% (95% CI -33.5 to -20.1) on the GAD-7. The corresponding threshold scores below which participants were more likely to report improvement were -1.7, -3.5 and -1.5 points on the PHQ-9, BDI-II and GAD-7, respectively. Patients with milder symptoms require much larger reductions as percentage of their baseline to endorse improvement. Conclusions An MCID representing 20% reduction of scores in these scales, is a useful guide for patients with moderately severe symptoms. If treatment had the same effect on patients irrespective of baseline severity, those with low symptoms are unlikely to notice a benefit. Funding Funding. National Institute for Health Research.

Automated summary

This study examined the Minimum Clinically Important Difference (MCID) for the Patient Health Questionnaire (PHQ-9), the Beck Depression Inventory (BDI-II), and the Generalised Anxiety Disorder Assessment (GAD-7). The findings suggest that for patients with moderate baseline severity, a reduction of 20% in scores represents an MCID. Patients with milder symptoms require larger improvements to notice a benefit.