Test | Student t-test | MEMA | |||||
---|---|---|---|---|---|---|---|
Gaussian | Laplacian | ||||||
Results | TS | TKH | TS | TKH | |||
Voxel 1 | Group effect | Estimate | 0.643 | 0.667 | 0.682 | ||
t | 4.542 | 5.006 | 5.153 | 5.942 | 5.443 | ||
pa | 0.0014 | 7.33e – 4 | 6.01e – 4 | 2.17e – 4 | 4.09e – 4 | ||
Cross-subjects heterogeneity | t̂2b | 0.200 | 0.0633 | 0.0296 | |||
Qc | – | 15.11 (0.0880) | |||||
H, I2d | – | 1.296, 0.406 | 1.149, 0.242 | ||||
Voxel 2 | Group effect | Estimate | 0.508 | 0.381 | 0.364 | ||
t | 3.89 | 5.536 | 4.705 | 7.334 | 5.156 | ||
pa | 3.67e – 3 | 3.63e – 4 | 1.11e – 3 | 4.40e – 5 | 5.98e – 4 | ||
Cross-subjects heterogeneity | t̂2b | 0.171 | 0.0177 | 0.0004 | |||
Qc | – | 18.49 (0.0299) | |||||
H, I2d | – | 1.30, 0.409 | 1.009, 0.018 | ||||
Voxel 3 | Group effect | Estimate | − 0.319 | −0.319 | −0.323 | ||
t | − 3.168 | − 5.020 | − 4.501 | − 4.564 | − 4.308 | ||
pa | 0.011 | 7.20e – 4 | 1.49e – 3 | 1.36e – 3 | 1.97e – 3 | ||
Cross-subjects heterogeneity | t̂2b | 0.101 | 0 | 0.007 | |||
Qc | – | 11.20(0.2622) | |||||
H, I2d | – | 1.0, 0.0001 | 1.081, 0.145 | ||||
Voxel 4 | Group effect | Estimate | − 0.193 | − 0.138 | − 0.138 | ||
t | − 5.449 | − 2.971 | − 3.915 | − 2.971 | − 3.915 | ||
pa | 4.1e – 4 | 1.57e – 2 | 3.54e – 3 | 1.57e – 2 | 3.54e – 3 | ||
Cross-subjects heterogeneity | t̂2b | 0.0013 | 0 | 0 | |||
Qc | – | 5.18 (0.8183) | |||||
H, I2d | – | 1.0, 0.0 | 1.0, 0.0 | ||||
Voxel 5 | Group effect | Estimate | 0.0496 | 0.0493 | 0.0493 | ||
t | 4.7152 | 0.8937 | 4.6376 | 0.8937 | 4.6376 | ||
pa | 0.0011 | 0.3947 | 0.0012 | 0.3947 | 0.0012 | ||
Cross-subjects heterogeneity | t̂2b | 1.1e-4 | 0 | 0 | |||
Qc | – | 0.3342 (1.0) | |||||
H, I2d | – | 1.0, 0.0 | 1.0, 0.0 |
Talairach coordinates (x, y, z) of the five voxels: (31, −91, −2) (Voxel 1), (−23, −89, 0) (Voxel 2), (−53, −17, 10) (Voxel 3), (−51, −11, 6) (Voxel 4), and (−5, 11, 0) (Voxel 5), where + x, y, z=RAS (neurological coordinates)
p-values for the t-statistics with 9 degrees of freedom are two-sided.
The variance for the conventional approach (paired Student t-test) is the estimated τ2+σ2 in the effect estimates, including both within- and inter-subject variances, assuming the within-subject variability being homogeneous in the group. The adjustment in TKH relative to TS does not involve the estimate of inter-subject variability τ2, which remains the same between the two tests.
The conventional approach assumes equal or no within-subject variance; thus, all the variability in the data is assumed to come between subjects. There is no way to test the significance of the inter-subject variability in the case of paired Student t-test under this assumption. The Q-statistic, defined in (8) for testing inter-subject variability (null hypothesis τ2=0), follows a χ2(9) distribution with the data at the five voxels (p-value shown within parentheses).
Approximate criteria for heterogeneity: H>1.5 (or I2>0.56), significant; 1.2<H<1.5 (or 0.31<I2<0.56), moderate; H<1.2 (or I2<0.31), negligible.