[Individual characteristics and biological rhythms. III. Utilization of a modified questionnaire to type morning and evening students].

A questionnaire modified in regard to that previously suggested by Horne and Ostberg has been utilized to distinguish the "morning" from the "evening" types. In 144 medical students it was found that almost 22% were evening type and 53% were morning type. By means of the new questionnaire there was an increment, percentagewise, of both groups from the 62% to 75%, indicating the usefulness of the method. The study of biological as well as psychological parameters should be pursued in order to control the validity of these results.