Application of factor analytic procedures to complex evoked potential measurements in psychiatric research

Several factor analytic procedures were applied to data gathered with a modified somatosensory evoked potential (SEP) recovery function prodecure in 56 non-patients and 224 psychiatric inpatients. The data were analyzed for each option reflected in three main issues. (1) Which group should be used for calculating the basic factor structure--normals only or all subjects? (2) Should measurements be preadjusted for covariance with variables known to obscure events of interest? (3) Should varimax rotation be used, or are principal components sufficient? Using two criteria, interpretability of factors in relation to experimental design, and their ability to discriminate clinical groups, it appeared that: (1) choice of either population yielded similar results; (2) when measurements were pre-adjusted for covariance more interpretable factors, which also yielded clinical discriminations, were obtained by varimax rotations than by principal components, and (3) when data were not adjusted by covariance, principal component analysis produced a factor which, although less interpretable in relation to experimental design than the varimax factors, provided equivalent clinical discriminations.