I see mentions of "But it's 1.8% failure rate!" - thing about Cumulative Probability is, that is a pretty high number of failure after about 10 years.
After 10 years you have a Cumulative Probability: P(X = 1) of about 15% of getting pregnant.
If you don't want to be a dad/mom - use a condom. Or go double dutch.
"Of 100 couples who use the symptothermal method correctly for one year, 0.4 (fewer than one) will have a pregnancy." (Source: http://www.plannedparenthood.org/health-topics/birth-control...)
So after about 100 years of using this method, you've got a .4% chance of becoming pregnant. Seems like decent odds to me.
No, after one year you've got a 0.4% chance of being pregnant. Assuming this stays steady over 100 years, you'd have a 33% chance of being pregnant (1 - (0.996 ^ 100))
Their maths for a 1.8% failure rate over 10 years is right, it's about 15%.
1. The same logic must be applied to condoms. They have a failure rate of 0.6 - 12% per year, depending on the study.
2. You mix perfect-use with imperfect-use. Even sterilization doesn't have a 0% failure rate, because sometimes things don't work out properly. The perfect-use index of sterilization should be 100% safety, but in reality, it's 99.9% I think.
Or the NuvaRing. Low hormone, can't forget it.
That means that if you have problems with one pill, you're very likely to have problems with other pills/hormonal methods as well.