Based on data from CDC study of American women's contraceptive status from 2011-2013.
How many women use natural family planning?
Not very many!
accurate “fertility awareness knowledge” (defined as knowing that there is a certain time in a woman’s menstrual cycle when she is most likely to become pregnant and being able identify that time as roughly halfway between her two periods)Looking through the links, I found that the survey asked if a woman was most fertile "before", "after", or "halfway between" periods. What a terrible way to ask! I'm not sure what I would have marked, since the best answer is "it depends." I suppose in a perfect 28 day cycle with ovulation on day 14, fertility would be roughly halfway, but few women have this perfect cycle. If a woman has a 21 day cycle, with ovulation on day 7-10, wouldn't "after" her period be the most sensible answer? And with my long 38 day cycles, treating "halfway" through my cycle as fertile would be a quick ticket to pregnant.