Some mathematical aspects of minimum trace factor analysis (MTFA) are discussed. The uniqueness of an optimal point of MTFA is proved, and necessary and sufficient conditions for any particular point to be optimal are given. The connection between MTFA and classical minimum rank factor analysis is discussed. (Author/JKS)

Psychometric data from two dyslexic groups were factor analyzed to identify dyslexic subtypes. Literacy, intelligence, auditory dysfunction, and visual/verbal dysfunction factors were identified. Results were discussed in the context of previous subtype classification studies. (Author/MJL)

The possibility of using a Q-analysis also for nominal data is discussed, using the J-index as a measure of similarity between persons. An example is given when ten persons sorted 16 playing cards into as many groups as they wished. A Q-analysis of these data gave a natural two-dimensional structure. (Author/BW)

A model for four-mode component analysis is developed and presented. The developed model, which is an extension of Tucker's three-mode factor analytic model, allows for the simultaneous analysis of all modes of a four-mode data matrix and the consideration of relationships among the modes. (Author/JKS)

It is proved for the common factor model that, under certain conditions maintaining the distinctiveness of each factor, a given factor will be determinate if there exists an unlimited number of variables in the model, each having an absolute correlation with the factor greater than some arbitrarily small quantity. (Author/JKS)

The G index and its generalizations in the six basic factor analytic designs are discussed. G should be used if there is no mutual direction of all the variables. G should also be used if the scale center is more suitable as a reference point than the mean value. (Author/CTM)