We show that Cohen’s Kappa and Matthews Correlation Coefficient (MCC), both extended and contrasted measures of performance in multi-class classification, are correlated in most situations, albeit can differ in others. Indeed, although in the symmetric case both match, we consider different unbalanced situations in which Kappa exhibits an undesired behaviour, i.e. a worse classifier gets higher Kappa score, differing qualitatively from that of MCC. The debate about the incoherence in the behaviour of Kappa revolves around the convenience, or not, of using a relative metric, which makes the interpretation of its values difficult. We extend these concerns by showing that its pitfalls can go even further. Through experimentation, we present a novel approach to this topic. We carry on a comprehensive study that identifies an scenario in which the contradictory behaviour among MCC and Kappa emerges. Specifically, we find out that when there is a decrease to zero of the entropy of the elements out of the diagonal of the confusion matrix associated to a classifier, the discrepancy between Kappa and MCC rise, pointing to an anomalous performance of the former. We believe that this finding disables Kappa to be used in general as a performance measure to compare classifiers.

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As suggested by previous research, the study of personality traits among sexual offenders could be an important consideration in the understanding of sexual offending. This study aims to explore the possibility of classifying sexual offenders according to their personality profiles. Based on the MCMI-III scores of 97 convicted contact sexual offenders, a cluster hierarchical analysis was performed. Next, the groups were characterized according to their sociodemographic and criminological variables and significant differences between them were sought. The two clusters found did not show different MCMI-III prototypical personality profiles, and both groups only varied in the degree of general psychopathology. The results suggest the existence of two personality profiles labeled as "pathological" and "adapted/non-pathological". The usefulness of the MCMI-III in the evaluation of sexual offenders seems limited to the detection of the presence or absence of general psychopathological symptoms. Implications of these findings for interventions are discussed.