The preferred range varies for salesmen of different kinds of products and also with the territories within which they operate. In many occupations it has been shown that there is no upper limit to the optimal intelligence score; but studies of policemen and of machine operatives, as well as of salesmen and of clerical workers where the task is essentially routine, have shown how necessary it is to keep an eye on the upper as well as the lower critical score, in order to avoid anomalous or ambiguous inferences.

Statistical Methods in Employment Psychology. In developing aids for selection and placement of workers, the statistical method of group differences has proved useful, particularly in evaluating items of personal history information which throw light on the applicant's character, temperament, and emotional adaptability to the work for which he is being considered. The method is simple enough in application.1 The groups compared are the successful and unsuccessful workers employed at the occupation in question; or those successfully engaged in the work, compared with a sample of the population at large. The proportion of each group answering an item on the application blank in a certain way, or making a certain critical score on a test, is ascertained. The difference in proportions is then computed, and also the standard error of this difference. If the difference in proportions is more than twice the standard error of the difference, it is considered to be significant for this purpose. Then the individual applicant's performance with reference to the item in question is given a weight corresponding to the size of this ratio, in the total score. Or, if the number of questionnaire items or test scores to be 1 Bingham and Freyd, "Procedures in Employment Psychology," Chaps, xiii and xv, McGraw-Hill Book Company, Inc., New York, 1926.

treated in this way is large, not much reliability is lost if each item which proves to be significant is given a weight of +1 or of - 1, as the case may be, in computing the total score.

Such a method serves to add to the value of items of information obtained on the application form or in personal interview, regarding age, schooling, previous experience, marital status, and many similar considerations which may or may not be significant indicators of probable success. It lifts the evaluation of such items out of the area of guesswork or subjective impression.1 The method is equally applicable to items obtained in the physical examination, such as height, weight, eyesight, strength, and blood pressure.

Preconceptions as to the importance of such facts about an applicant have sometimes been modified or even reversed when sufficient data have been gathered and the computations made. As an illustration may be cited a study of a group of young women operators made by the writer in one of the plants near New York City. They were engaged in tending machines which wind paper insulation about strands of copper wire for making telephone cables. These machines make a deafening noise, yet the girls work here month after month and do not seem to mind it. Their minimum wage is thirty-eight cents an hour, but the most skillful operatives among them are able to increase this rate to as much as sixty or sixty-five cents. Even during the period of learning the work they receive a better wage than the average high-school graduate who goes into an office as a typist, and after two to eight months the more competent ones earn more than a college graduate usually does during her first year in an office. The work is not 1 Manson, Grace E., What Can the Application Blank Tell? Evaluation of Items in Personal History Records of Four Thousand Life Insurance Salesmen, Journal of Personnel Research, Vol. 4, pp. 73-99, 1925.

wholly unlike that of tending spindles in a cotton mill. It calls for some skill, strength, and mental alertness; but it seems to require in addition a certain stolidity and poise which enables the operator to keep steadily at work when the paper breaks on two or three heads at about the same time. If she is high-strung, she becomes nervous or excited under these circumstances, so that matters go from bad to worse; whereas if she is not tense or irritated, she gets out of trouble more quickly. Her output is less likely to suffer. She makes better wages, and is apt to be more contented and to continue at the work.

The problem of vocational selection for such a job pointed toward the more precise utilization of information already being gathered on the application form, in personal interview and in the medical examination. A check-up of items was made in order to determine which were really significant in sorting the successful from the unsuccessful operators. For purposes of this study an operator was classed as successful if she proved to be both able and willing to stay on the job for six months. An unsuccessful operator was defined as one who disappeared from the payroll within that period. The main group studied consisted of all operators hired during a period of sixteen months, totaling 246 young women. Of these, 43 per cent became successful operators in the sense indicated. Data regarding them were drawn from the tabulation cards of the employment department, from the application blanks, and from the files of the medical examiner. For each item for which information was recorded, a comparison was made between the successful and unsuccessful operators. Wherever differences appeared, the percentage of each group falling within the preferred range was computed and the significance of differences in percentages determined.

On most of the items there was no discoverable significant difference between the successful and the unsuccessful operators. For instance, we could find no preference for tall girls or short girls, or girls of medium height. There was about the same proportion of any particular height in the unsuccessful as in the successful group.