OBJECTIVE: Previous research on the minimal clinically important difference (MCID) for depression and anxiety is based on population averages. The present study aimed to identify the MCID across the spectrum of baseline severity.
STUDY DESIGN AND SETTINGS: The present analysis used secondary data from two randomised controlled trials for depression (n=1,122) to calibrate the Global Rating of Change with the PHQ-9 and GAD-7. The MCID was defined as a change in scores corresponding to a 50% probability of patients "feeling better", given their baseline severity, referred to as Effective Dose 50 (ED50).
RESULTS: MCID estimates depended on baseline severity and ranged from no change for very mild up to 14 points (52%) on the PHQ-9 and up to 10 points (48%) on the GAD-7 for very high severity. The average MCID estimates were 3.7 points (23%) and 3.3 (28%) for the PHQ-9 and GAD-7 respectively.
CONCLUSION: The ED50 method generates MCID estimates across the spectrum of baseline severity, offering greater precision but at the cost of greater complexity relative to population average estimates. This has important implications for evaluations of treatments and clinical practice where users can employ these results to tailor the MCID to specific populations according to baseline severities.
Bibliographical noteFunding Information:
PANDA was funded by the National Institute for Health Research Programme Grant for Applied Research (RP-PG-0610-10048). CoBalT was funded by National Institute for Health Research Health Technology Assessment (Project Number 06/404/02). The research was supported by the NIHR Biomedical Research Centre at the University Hospitals Bristol NHS Foundation Trust, the University College London Hospital NHS Foundation Trust and the University of Bristol. The views expressed in this publication are those of the author(s) and not necessarily those of the Sponsor, NHS, NIHR or Department of Health, and Social Care. The funder had no role in the study design, data collection, data analysis, interpretation of data or writing of the present manuscript. We would like to thank all involved in participating, conducting or otherwise supporting both RCT and are grateful to all co-applicants of the RCT who were not involved in drafting the present manuscript.
- minimal clinically important difference
- primary care
- clinically meaningful change