PREPROCESSING BY FACTOR-ANALYSIS OF CENTRO-OCCIPITAL EEG POWER AND ASYMMETRY FROM 3 SUBJECT GROUPS

Principal components analysis with Varimax rotation was applied to centro-occipital EEG power spectral density (PSD) and asymmetry variables in order to detect the subsets of intercorrelated variables. Seven orthogonal variable subsets (factors) were found: left and right PSDs from 0 to 8, 6 to 12, 12 to 20, and 12 to 30 Hz, and asymmetries from 0 to 6, 6 to 14, and 14 to 30 Hz. Attempts to validate these results suggest that the factors are satisfactorily orthogonal and account for a large part of the original data variance. The same set of factors appears to be present in normal subjects, stabilized alcoholics, and some chronic schizophrenics. More effective use of multivariate data in later statistical tests may be made possible by replacing the original variables with the factor scores computed from a weighted sum of the variables in the factors. Also, factor extraction allows comparison of the variable organization in different subject groups. This can have both physiological and statistical significance.