No I disagree...and being an RN for 27 years, I might know a little bit about the subject. If a woman is very attuned to her self maybe....but I know many folks who’ve tried the natural methods but became pregnant anyway. Also the Song of Solomon has a lot to say about the love between a man and a woman, and nothing about the end result of such love simply being about children. Lot’s of lovin’ in the Song of Solomon but nothing about kids at all in the whole book.
And you realize that "data" is not the plural of "anecdote" :o)
The solid research is unanimous on the effectiveness of NFP being fully on a par with the oral contraceptive pill, >99%. It has practically no "method failures" when used correctly.
That last part, "when used correctly," is important, since no method will work when used incorrectly. A condom isn't very good if you put it on your nose; NFP isn't very good if you're just trying to guess or predict ovulation, as opposed to actually observing real-time signs of impending ovulation. Your "many folks who tried the natural methods" possibly were guessing and predicting, and not doing actual Sympto-Thermal Method (STM) type NFP, or possibly did know when they were in the cycle and had intercourse knowing they were fertile. This latter case is not method failure: this is called "successfully achieving pregnancy through NFP."
Ross Pomeroy, a zoologist and science journalist who is derisive of the Christianity and dismissive of moral considerations in general, still admits that
"A large study conducted in 2007 found that the "symptothermal" method of natural family planning, in which the female user tracks both her body temperature and cervical secretions to gauge her fertility, is 99.6% effective when properly adopted, roughly the same as a copper intrauterine device.The Oxford Journal's Human Reproduction issue found 0.6 per 100 women and per 13 cycles when there was no unprotected intercourse in the fertile time (LINK) --- in other words, a 99.4% method effectiveness rate.
If you want to do a real survey of the studies, here's a huge list of studies, most (but not all) in English (LINK)
Personally, I wish everyone knew about this. It's literally God's gift to women.