QuestionHi Dr.:
Thank you for your prompt reply.
I ended up coming across the following article:
http://humrep.oxfordjournals.org/content/17/5/1399.short
and in fact corresponded with the author in relation to the issue of why one of the other papers he had co-authored with Wilcox had a 33% chance of pregnancy on the peak day of fertility whereas, his article had a probability of in excess of 50% on the peak day of fertility for women 18-25.
He indicated that the fecundity rate for women is not homogenous. Further, he indicated like you did that studies can be different based on populations being examined and the size of the study eg. in his earlier paper with Wilcox, the women were coming off birth control medication whereas the above paper related to natural planning.
He concluded by saying that it is unclear why there were differences. In essence, just as he did in the above noted paper.
AS AN ASIDE, HOW DID THE AUTHOR IN THE ABOVE PAPER DETERMINE PERCENTILE OF FERTILITY, eg. Figure 3 how do you determine that a particular woman is in the 5th percentile of fertility vs the general population and another woman is in the 95th percentile of fertility?
AnswerIt's my understanding that the authors take the percent of women getting pregnant on each day as percentile of fertility, rather than that any individual woman is in the 5th percentile. It doesn't make sense to me to say a particular woman is in the 5th percentile.
