Hierarchical empirical Bayesian inference on group effects using the function spm_dcm_peb. Hierarchical empirical Bayesian inference on group effects using the function spm_dcm_peb. A, Results of Bayesian model comparison (reduction) to infer whether the full model (with both group mean and group differences) or a reduced (nested) model (bottom left) provides a better explanation for the data. These results indicate high posterior evidence for a model with a group difference, with slightly less evidence for the full model, which also includes a group mean effect (i.e., a deviation from the group prior mean; top panels). Middle panels show the maximum a posteriori estimates of the mean and group effects for the full and reduced models. B, Estimated (gray bars) group mean (left) and difference (right) in β. These estimates are about one-quarter (top right), which corresponds to the group effect that was introduced in the simulations (black bars). The small bars correspond to 90% Bayesian confidence intervals. A reduced parameter estimate corresponds to the Bayesian model average over all possible models (full and reduced) following Bayesian model reduction. Philipp Schwartenbeck, and Karl Friston eneuro 2016;3:ENEURO.0049-16.2016 ©2016 by Society for Neuroscience