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I have to report the results of a study which is of interest because of the further confirmation it gives to Freud's original three-stage division of the individual's psychosexual development, and because of its value in showing the possibilities of the statistical method in the investigation of psychoanalytic problems.
The study consisted of the simple procedure of observing and then recording the frequency of fingernail biting among children, at different ages. For this purpose I made observations on some 3,000 children of both sexes, ranging from one to seventeen years in age. The subjects were for the most part children attending the New York public schools or in the case of the very young ones, of infants at public nurseries. The children of school age were asked to place both hands, palms downward, on their desks, and as the examiner passed he noted on a slip of paper previously prepared, and having on it the name, age and sex of the subject, the fact whether there was or was not any evidence of fingernail biting. A plus sign indicated that the child did, and the minus sign that it did not bite its nails. These slips were then sorted as to age and sex and tabulated in a manner presently to be indicated. In the case of the nursery children the examiner recorded the presence or absence of nail biting directly as the children filed by him. Owing to the smallness of the number of cases the children were not separated as to sex in recording the cases up to four years of age.
The children examined represented quite a random and diverse sample of the normal school population, being derived from schools in all parts of Manhattan, and representing nearly all racial groups and social levels. No distinction was attempted as regards degree of biting and those marked plus ranged from cases where there was evidence of only occasional biting, say of a single finger, to those of inveterate biting of practically every finger of the hand. The disregard for this quantitative diffe