“Isn’t 99% about the same as pharmaceutical birth control?”
No, not even close... With pharmaceutical birth control, it’s a little over 99% when the female is fertile. It ends up being an order of magnitude difference.
How is 99% an order of magnitude different from 99%?
British Medical Journal, Sept 18, 1993 v307 n6906 p723(4)
"Natural family planning":
Effective Birth Control Supported by the Catholic Church
R.E.J. Ryder.
Abstract:
Natural family planning, when used by motivated couples, is a safe and cost-effective means of birth control. Natural family planning, which involves teaching women to recognize signs of ovulation and to avoid intercourse on fertile days, is the only method of birth control approved by the Catholic Church. A total of 869 women of diverse ethnic and economic backgrounds participated in a study conducted by the World Health Organization. Regardless of literacy and culture, 93% of the women were able to recognize the changes in their cervical mucus associated with ovulation. Other studies have emphasized the importance of good initial teaching and the motivation of the woman practicing the method. A failure rate of 0.2 pregnancies per 100 women was found in a study of 19,843 women in India.
...The largest natural family planning study combined effective teaching with high motivation and showed that natural family planning can be extremely effective in the Third World.[33] The study was of 19 843 predominantly poor women in Calcutta, 52% Hindu, 27% Muslim, and 21% Christian. Because of poverty motivation was high both among the users and among the well trained teachers of natural family planning. The failure rate was similar to that with the combined contraceptive pill--0.2 pregnancy/100 women users yearly.[33] The result suggests that poverty as the motivation can greatly improve the effectiveness of natural family planning. A similar result, however, was achieved in Germany in a study with a pregnancy rate of 0.8.[34]
An Italian study found an overall pregnancy rate of 3.6, all the pregnancies occurring in couples wishing to space but not limit their families. The pregnancy rate was zero in couples who wanted no more children.[30] With other German studies finding pregnancy rates of 1.8[31] and 2.3,[36] a study in general practice in the United Kingdom finding a rate of 2.7,[39] and a study among 3003 illiterate and semiliterate women in India yielding a pregnancy rate of 2.04[37] the accumulating data confirm that natural family planning can be as effective as any method of family planning.