Table 4.

Estimated sample sizes^* for clinical trials using change in regional volumes as an outcome measure

	Far				Mid				Near
	Effect size difference from controls	Expected therapeutic effect**			Effect size difference from controls	Expected therapeutic effect**			Effect size difference from controls	Expected therapeutic effect**
		50%	40%	30%		50%	40%	30%		50%	40%	30%
Caudate	− 0.33	749	1171	2082	− 0.81	126	197	350	− 0.60	235	366	652
Putamen	− 0.25	1366	2134	3794	− 0.60	233	363	646	− 0.63	211	329	585
Total striatum	− 0.39	535	835	1485	− 0.87	111	173	307	− 0.75	147	230	409
Thalamus	− 0.06	27783	43411	77176	− 0.36	661	1032	1835	− 0.46	397	620	1103
Globus Pallidus	− 0.43	454	710	1262	− 0.27	1154	1803	3205	− 0.67	188	294	523
Cortical gray	+ 0.17	3094	4834	8594	+ 0.22	1739	2717	4829	+ 0.11	7799	12185	21663
Cerebral white	− 0.49	343	535	951	− 0.89	106	166	295	− 1.17	61	96	171
Total brain	− 0.33	748	1169	2078	− 0.62	216	338	601	− 0.98	87	136	242
Ventricular CSF	+ 0.31	879	1374	2443	+ 0.67	188	294	524	+ 1.20	59	92	163
Surface CSF	− 0.11	7697	12027	21381	+ 0.25	1309	2045	3636	+ 0.52	303	474	842
Total CSF	+ 0.05	36241	56627	100671	+ 0.35	691	1080	1920	+ 0.69	179	280	497
Frontal white	− 0.54	286	447	795	− 0.86	112	175	311	− 1.15	63	98	174

^*N per treatment arm for a two-year clinical trial, assuming two-sided alpha = 0.05; 90% power

^**% reduction in rate of case-control atrophy difference.