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In planning this experiment it was deemed wise to select tests which have already been used by psychologists to measure relatively small differences, and which have been found to be susceptible to a wide variety of influences. Two motor tests were therefore selected on this basis, -- the familiar tapping test, and a steadiness test; and two mental tests, -- color naming and saying opposites. A measure of motor fatiguability was also included, and tests were made of speed and accuracy in typewriting. It would be, of course, highly desirable to perform experiments for sensory capacity, suggestibility, reaction time, endurance in working for long periods, but it was not possible to include all these within the scope of the present study.

The tests were given daily, under uniform conditions; at the same hour (immediately after dinner in the evening), by the same person, and in the same order. They were simply included among the regular routine duties of the subjects. Any unavoidable departure from the strictly usual, such as a slight difference in the hour of testing, headache on the part of any subject, nervous strain during the day, such as a visit to the dentist, was recorded.

It was impossible to get several subjects to undergo this long, rigidly conditioned series of tests during the same months. Subjects had to be taken when they could be had for several months without interruption, every day at the same hour. It was not easy to find normal women who could and would conform to these conditions, without compensation and without information as to what the object of the work might be. The tests therefore extend over four separate series of months.

The first series of tests (on subjects M1, F1 and F2) began on December 21, 1912, and ended March 30. 1912. One record was made daily for each subject in each test until March 3d. It was then thought that a more reliable measure of efficiency [p. 12] on a given day could be obtained, and thereafter two trials daily were taken, the first at the same hour as previously, and the second just before retiring for the night. Thus after March 3d, each record is the average of two trials.

The second series of tests (on subject F3) began September 29, 1912, and ended January 7, 1913. Each daily record in each test for F3 is the average of two trials. The test for fatiguability (on subjects M1, F2 and F3) was also carried out during the same months in which the tests on F3 were made.

The third series of tests (on M2 and F4) began on April 19, 1913, and ended on June 12, 1913. Each record in each test for M2 and F3 is the average of two trials.

The fourth series of tests (on subject F6) began November 13, 1913, and ended February 5, 1914. Each record in each test for F6 is the average of two trials.

There were eight subjects, six women and two men.

F1 was a woman 23 years of age, a student and a teacher of music. She was entirely naïve to the experiment, having no idea of the purpose involved. This subject never suffered at physiological periods.

F2 was a woman 25 years of age, a university graduate student. She knew the purpose of the experiment, but had no preconceived notion as to how any particular test would be affected. This subject occasionally experienced some pain for a few hours on the first day of the period, and it may be added here that this was the case on January 5th and February 1st, but not on the other first days included in this record.

F3 was a woman 24 years of age, a college student whose profession was teaching. She, like F1, was entirely naïve to the experiment, having no idea whatever of the purpose of the tests. This subject very rarely experienced discomfort at physiological periods, and did not at any period included in this report.

F4 was a woman 36 years of age, the mother of two children. This subject was also a teacher, and as such had led a professional life for ten years before her marriage. She knew the purpose of the experiment, and had the preconceived idea that she would prove to be less steady during menstruation. She had no preconceived notion as to the outcome of the other tests.[p. 13] F4 regularly experienced an attack of neuritis just before each period, due to a pathological condition of which she was cognizant, and frequently had a premonitory headache. During the period itself this subject did not suffer.

F5 was a woman 24 years of age, the mother of one child. She was a college graduate, but had never led a professional life. She knew the purpose of the experiment, but had no preconceived idea as to the outcome of the test. This subject took part only in the experiment on typewriting. She never suffered at menstrual periods.

F6 was a woman 45 years of age. This subject had had one child. She was a university graduate, and before her marriage she had been a teacher. She knew the purpose of the experiment, but had no preconceived ideas as to the probable outcome of any of the tests. She was passing through the climacteric, and to this fact is due the irregularity of occurrence and duration in the critical periods included in her record. This subject reported "no pain" at every one of the three periods included. She reported "very tired" on the first day of the first period, and on the fourth day of the third period, the same report being also made on days when the subject was not menstruating.

Two men took the tests in exactly the same way as the women subjects, thus yielding a control record. M1 was 31 years of age, and M2 was 37 years of age. Both were trained psychologists, and both led professional lives. Both were in excellent mental and physical health.

These women (except for the recurrence of neuritis in the case of F1) presented conditions of normal menstrual health, and all were in excellent mental health. None of them (except F4) experienced headaches or other nervous symptoms at periods, and they were not accustomed to remit work or make changes in their usual programmes of occupation. F2 and F3 were sisters. F1, F4, F5 and F6 were not related to them nor to each other in any way. The exact occurrence of physiological periods was indicated by placing a star (*) on the records taken on the days comprising each period. For F1, F2 and F3 the period presumably affected was five days in duration; for F4, sometimes five and sometimes four days; for F5, six days; for F6, sometimes five and sometimes three days.[p. 14]

It is regrettable that daily records could not have been taken on a much greater number of subjects (both men and women). The intensive work with eight subjects is, however, supported and extended by similar experiments made on seventeen women, each of these subjects being tested on every third day for a period of thirty days. This additional work will be reported in a subsequent section of this monograph. The intensive study of the eight subjects who were tested daily is based on about 4,500 precise observations. The experiments were performed with the following questions in mind:

(1) Will careful and exact measurement reveal a periodic mental and motor inefficiency in normal women?

(2) If inefficiency be found, is it a function of physical suffering, or of profound psychological change, occurring independently of pain?

(3) If inefficiency be found, is it characteristic of the whole period, or only of a part of it?

(4) Is there greater or less variability of performance on days presumably affected?

(5) Is it possible to discern a period of regularly recurring maximum efficiency in each month?

(6) Is it possible to find, by methods of precision, the cycle referred to by Ellis and others?

(7) Can any relation be established between the curves platted for pulse-rate, blood pressure, temperature, etc., and the curves of a daily mental or motor performance extending over several months?