From The Shadow Exploded (p. 41):

Both medical and psychological writers on the subject are in agreement that Carrie White's exceptionally late and traumatic commencement of the menstrual cycle might well have provided the trigger for her talent.

In fact, it is possible to argue persuasively, based on both clinical observation and careful analysis of available data, including the results of recent experiments, conducted by Dr. Edward F. Sledge, Ph.D., associate professor of psychology at Columbia University, New York City, N.Y.

Dr. Sledge has argued convincingly, for example, against any suggestion of hysteria in Carrie White. His findings, published in The Journal of Abnormal Psychology, Vol. 48, No. 1, pp. 62-68, Jan.-Feb. 1958, make a strong case for a psychogenic origin to the phenomena.

He also suggests further research along the lines he outlines below:

(1) If the hypothesis advanced here regarding the relationship between menstruation and telekinetic activity holds true, then one should find certain characteristics common to all persons who display the power.

If telekinesis occurs most frequently during periods of emotional distress, it follows logically, I believe,

(2) Such individuals would tend to show symptoms of heightened anxiety through menses and/or shortly before its onset, and

(3) Conversely, persons whose moods are relatively stable during those times would probably not demonstrate telekinetic powers.

This last item will require considerable testing, but it certainly seems logical. One would expect to observe the same tendencies in the various groups listed above, such as those described by Leland Clark in his book, "Telekinesis."

Since this is a field in which little work has yet been done, however, we cannot be absolutely sure of the validity of that line of reasoning until more experimental evidence can be obtained.