The minimum clinically important difference (MCID) for a falls intervention in Parkinson's: A delphi study

Background: Falls are common in Parkinson's disease so any intervention that reduced falls risk would be of value. One potential intervention is the use of cholinesterase inhibitor (ChEi) drugs. Objective: To establish the minimum clinically important difference (MCID) for fall rates to inform the effect estimate for sample size calculations of future clinical trials. Methods: We performed a Delphi study assembling a panel of experts in Parkinson's disease from academic and clinical medicine in order to reach a consensus of opinion. Responses from a panel were summarised and resent to the group, until consensus was reached. Results: 780 clinicians, who had been caring for people with Parkinson's for an average of 14 years, were contacted via three routes. The median (Interquartile range (IQR)) MCID after round 1 was 25% (IQR 20-30%) which equates to the prevention of 5 (IQR 4-6) falls per year. Increasing consensus after round two confirmed the MCID of 25%, narrowing the (IQ) range to 20%-25%. This was unchanged when the panel were shown the number of participants that would need to be recruited to a clinical trial in order to achieve this difference. Conclusions: We have established that an expert panel of PD specialists consider that an intervention that demonstrated a 25% (IQR 20-25%) relative reduction in falls rate would be clinically meaningful. This estimate can be used to help determine the sample size for any future clinical trial.