A study that appeared in the June 2009 edition of the journal Contraception revealed that there are only minor differences in pregnancy rates between withdrawal and the use of condoms as method of contraception.
This means that withdrawal before ejaculation during intercourse is not an ineffective method for contraception. The study also finds that about 18% of couples will become pregnant in a year using withdrawal, while male condoms have a 17% failure rate.
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CBS News

Hey, ok, I get it, I guess – but does this really work?
Damn, that sound’s so easy if you think about it.