Fecundability Estimates Some comments on M. Henry's paper.

The article discusses author's comment on the article "Some Comments on W.H. James's Article," by M. Henry in the November 1964 issue of the journal "Population Studies." M. Henry suggests modifications to the author's estimates to make them directly comparable with previous estimates. He concludes that there remains a disparity and to account for this he offers theoretical criticism of the methods used by the author in the study and objects to the values assigned to the mean duration of post-partum sterility. In modifying the author's estimates he considers the effect of spontaneous abortion. Author's study suggested that the probability of a woman's aborting might not increase much as she grows older. It seems possible that the apparent increase, or the greater part of it, could be explained as due to a statistical artifact. In any case it seems that M. Henry is providing an inappropriate factor to make the author's fecundability estimates comparable with earlier estimates based on conception waits.