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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.