Effective dose 50 method as the minimal clinically important difference: Evidence from depression trials.
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 2 randomized 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 use these results to tailor the MCID to specific populations according to baseline severities.
['Bauer-Staeb|Clarissa|C|', 'Kounali|Daphne-Zacharenia|DZ|', 'Welton|Nicky J|NJ|', 'Griffith|Emma|E|', 'Wiles|Nicola J|NJ|', 'Lewis|Glyn|G|', 'Faraway|Julian J|JJ|', 'Button|Katherine S|KS|']
D000328:Adult D001007:Anxiety D003863:Depression D005260:Female D006801:Humans D008297:Male D008875:Middle Aged D000071081:Minimal Clinically Important Difference D012720:Severity of Illness Index
Minimal Clinically Important Difference MCID PHQ-9 GAD-7 Clinically Meaningful Change Primary Care