Taking chances?

Advocates of the OM (ovulation method) of contraception attempt to explain the high OM user pregnancy rates, about 39/100 woman-years (compared to 13/100 with the sympto-thermal method), saying that too many users are taking chances and engaging in coitus during quasi fertile or fertile days. This cannot be so since pregnancy achieving behavior, or taking chances, can be applied to OM users as well as to STM users, or, for that matter, to pill, IUD, or diaphragm users. A contraceptive method is of little use when theoretical effectiveness is excellent, as in the case of OM, but practical dependability is very poor. The combined use of OM, and of the temperature method is called to sympto-thermal method; it makes use of the best of both methods, and it provides for cross-checking of all symptoms.