Table 3.

Estimated sample size required per treatment arm in a one year parallel group clinical trial for imaging and clinical outcomes, incorporating 23% attrition rate.

Effect size	Imaging outcome measures				Clinical outcome measures
	Whole brain	Ventricular volume	Midbrain	SCP	PSPRS	RBANS	SEADL
10%	2222	788	870	2606	868	1532	1132
25%	358	130	139	417	142	249	184
37.5%	151	60	64	188	65	112	83
50%	87	35	36	108	38	65	48

SCP = superior cerebellar peduncle, PSPRS = progressive supranuclear palsy rating scale, RBANS = repeatable battery for the assessment of neuropsychological disease severity, SEADL = Schwab and England activities of daily living.