Physiologic effectiveness is the measure of protection against unwanted pregnancy afforded by a specific contraceptive method under ideal conditions ie, used consistently and according to instructions-without omissions, or errors of technique. Such ideal conditions are rarely present. Even when they are, it is not practicable to observe and verify them. Physiologic effectiveness, although not accessible to direct measurement, is by definition higher than the observed clinical effectiveness of the same method in the hands of the most …