Do QEEG topographic map data have a multivariate normal distribution? Implications for tests of individual maps.

The study was designed to test whether topographic map data expressed in log power units have a multivariate normal (MVN) distribution in a healthy population, and to determine if any deviation from normality poses serious difficulties for the use of standard multivariate statistical tests in assessing the significance of deformations of the map in individual cases. Data on 361 healthy adults using 20 electrodes in the classic 10/20 configuration were recorded in six frequency bands. The log-transformed power data were shown to deviate markedly from MVN. The actual distributions of multivariate tests were computed for the sample using the 'jackknife' method, and shown to deviate markedly from the F-distributions that would be expected for MVN data. These 'jackknife' sampling distributions were then used to demonstrate significant deformations in the topographic maps of a patient who had sustained traumatic head injury.