A note of correction with reference to parameters of the menstrual cycle and the efficiency of rhythm methods of contraception

Abstract

Owing to a misunderstanding in regard to the data sheets, all the references to the pre- and post-ovulatory phases in Dr. Marshall's data in my paper should be interchanged. The following is a list of conclusions which may be drawn from that study:

1.	Although the Farris Test is probably less efficient than had formerly been thought, there is no evidence that it is biased.
2.	Within individual histories, pre-ovulatory phase variance usually exceeds post-ovulatory phase variance.
3.	The variance of mean pre-ovulatory phase exceeds that of mean post-ovulatory phase among a group of women.
4.	Within a group of women, there seems to be no appreciable correlation between mean pre-ovulatory and mean post-ovulatory phase.
5.	It is possible that there is a true underlying positive correlation between pre- and post-ovulatory phases within a single menstrual history.
6.	The standard error of the RB.T. test was estimated to exceed √6 days.
7.	The variances of the phases within individual histories are probably positively correlated, so it seems that in general a variable post-ovulatory phase is not favourable to the outcome of the practice of rhythm.