Table 2.

Sample Size Estimations for the Detection of Disease Modification in a Hypothetical 1‐Year Placebo‐controlled Clinical Trial

Symptomatic Change in Treated Group	Mean Change in MDS‐UPDRS Part III in Treated Group at 1 Year (Treatment Effect, % Attenuation)*	Total Sample Size [Per Group]
Slowing of progression	+4 (−2.35, 37%) +2 (−4.35, 69%)	480 [240] 142 [71]
Halting of progression	0 (−6.35, 100%)	68 [34]
Reversal of progression	−2 (−8.35, 131%) −4 (−10.35, 163%)	40 [20] 28 [14]

Abbreviations: MDS‐UPDRS: Movement Disorder Society‐Sponsored Revision of the Unified Parkinson's Disease Rating Scale.

Calculations were based on assumptions of 90% power; a mean ± standard deviation progression of 6.35 ± 6.66 points on MDS‐UPDRS Part III for the untreated (control) group, as observed in Parkinson's Progression Markers Initiative (PPMI) participants who were not taking dopaminergic medication at 1 year; and a standard deviation of 9.00 points on MDS‐UPDRS Part III for the treated group, as observed in PPMI participants who were taking dopaminergic medication at 1 year. Sample size was allocated equally to the treatment and control groups and assumed that data from all participants were valid and usable.