Oral contraception, oral contraceptive pill
"How effective is the oral contraceptive pill?
If you take the contraceptive pill as instructed, it is over 99% effective. This means that if 100 sexually active women who are otherwise healthy take the pill as instructed for a year, only one of them will fall pregnant"
Whereas
http://www.nice.org.uk/nicemedia/pdf/CG030costing.pdf
Table 7 shows an annual failure rate of 8%
Both are true - it's the "if" in the first one that is perhaps misleading.
Jeff


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