Table 4:

Minimal sample size required to detect a 2% 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	896	80.0	11	80.5	38	80.8
L frontal GM	898	80.0	20	81.5	72	80.4
R frontal GM	956	80.0	15	80.8	54	80.9
L occipital GM	1050	80.0	28	80.6	106	80.6
R occipital GM	1016	80.0	28	80.2	106	80.2
L parietal GM	1022	80.1	22	81.2	80	80.2
R parietal GM	1056	80.1	33	81.2	124	80.6
L temporal GM	1130	80.1	42	80.5	162	80.5
R temporal GM	1262	80.0	49	80.3	190	80.3
L frontal WM	824	80.1	30	80.5	114	80.5
R frontal WM	998	80.0	30	81.0	112	80.3
L occipital WM	2246	80.0	130	80.1	514	80.1
R occipital WM	1730	80.0	105	80.3	412	80.1
L parietal WM	1190	80.1	29	80.9	108	80.2
R parietal WM	926	80.0	33	80.2	126	80.2
L temporal WM	1448	80.0	70	80.5	272	80.2
R temporal WM	1580	80.0	70	80.2	274	80.1
L caudate	1298	80.0	280	80.0	1116	80.1
R caudate	1506	80.0	324	80.1	1290	80.1

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.