[Individual characteristics and biological rhythms. I. Morning and evening subject typing based on cluster analysis].

The Horne and Hostberg questionnaire to differentiate "morning" and "evening" types was adopted to study the morningness-eveningness in I44 medical students. Furthermore the reliability of the proposed typology was assessed by using the cluster analysis, which partially confirmed the categories of Horne and Ostberg, since the clusters were characterized by the presence of subjects belonging to different types. No difference by sex was observed by either method. By means of the cluster analysis it was possible to identify 20% of evening and 40% of morning types.