Combined permutation test and mixed‐effect model for group average analysis in fMRI

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Abstract
In group average analyses, we generalize the classical one‐samplettest to account for heterogeneous within‐subject uncertainties associated with the estimated effects. Our test statistic is defined as the maximum likelihood ratio corresponding to a Gaussian mixed‐effect model. The test's significance level is calibrated using the same sign permutation framework as in Holmes et al., allowing for exact specificity control under a mild symmetry assumption about the subjects' distribution. Because our likelihood ratio test does not rely on homoscedasticity, it is potentially more sensitive than both the standardttest and its permutation‐based version. We present results from the Functional Imaging Analysis Contest 2005 dataset to support this claim. Hum Brain Mapp 27:402–410, 2006.