Table 3:

Minimal sample size required to detect a 5% change in volume with at least 80% statistical power, under a variety of assumptions about study design*

Structure	Cross-Sectional		Longitudinal		Longitudinal
	2 Groups		1 Group		2 Groups (change)
	No.	Power	No.	Power	No.	Power
Whole brain	146	80.3	4	86.7	10	90.2
L frontal GM	146	80.2	5	80.0	14	82.3
R frontal GM	156	80.4	5	90.0	12	86.5
L occipital GM	170	80.1	7	86.0	20	83.3
R occipital GM	166	80.4	7	85.6	20	82.9
L parietal GM	166	80.3	6	87.1	16	84.0
R parietal GM	172	80.4	7	80.3	22	81.3
L temporal GM	184	80.4	9	83.2	28	81.0
R temporal GM	204	80.1	10	82.2	32	80.1
L frontal WM	134	80.2	7	83.4	20	80.4
R frontal WM	162	80.2	7	83.8	20	80.9
L occipital WM	362	80.1	23	81.1	84	80.2
R occipital WM	280	80.3	19	81.4	68	80.3
L parietal WM	192	80.0	7	85.0	20	82.2
R parietal WM	150	80.1	8	86.2	22	80.3
L temporal WM	234	80.1	13	80.7	46	80.9
R temporal WM	256	80.3	13	80.4	46	80.5
L caudate	210	80.1	47	80.5	180	80.0
R caudate	244	80.3	54	80.4	208	80.0

Note:—L, left; R, right; GM, gray matter; WM, white matter.
* Estimated statistical power is shown for a sample size that was calculated to yield at least 80% power.