Alexander discusses the faults of the statistical approach in psychiatry and psychology, pointing out that replies given are rationalizations, which hide active unconscious motives. The questionnaire method is valid in the investigation of problems where the conscious attitudes are decisive. Where personal relations towards the same or opposite sex are involved unconscious factors are of primary importance and the psycho-analytic approach is necessary.

Of scientific investigation the first place belongs to the experimental technique, the second to comparative analytic studies, and the third to statistics which are the least satisfactory.