For statistical comparisons, the electrode sites were grouped into six scalp regions, and six representative electrodes from each region were included in the analysis (see Fig. 2; highlighted channels). The evoked power values obtained for the delta, theta, slow alpha, and fast alpha frequency bands were analyzed using a linear mixed-effects model of SAS Proc Mixed Procedure (SAS 9.3, SAS Institute Inc., NC, USA). The mixed-effects model included group (2: controls, alcoholics), condition (2: Go/NoGo), region (6: frontal, central, parietal, occipital, left temporal, and right temporal), electrode (6: representative electrode sites nested within each region) and their interactions as fixed effects, where condition (Go/NoGo) and electrode coordinates (x, y, z) were treated as repeated measures. To determine direct (Kronecker) product structures based on distance between electrodes (i.e., x, y, z), a spatial anisotropic exponential (EXPA) matrix was used to model within subject covariance structure of the data. A backward stepwise method was used to remove insignificant effects. Further exploration of main and interaction effects was performed using Wald's tests (Kenward and Roger, 1997) for pairwise comparisons and the significance levels
