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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.