Theoretical failure rate of 100 typical users who start out the year employing a given method, the theoretical failure rate is the number who will be pregnant at the end of the year.
Actual failure rate of 100 women who start out the year using a given method, and who use it correctly and consistently, the actual failure rate is the lowest observed failure rate.
| Theoretical Failure Rate | Actual Failure Rate | |
|---|---|---|
| Tubal Ligation | .04 | .04 |
| Vasectomy | .15 | .15 |
| Injectible Progestin | .25 | .25 |
| Combined Birth Control Pills | .5 | 2 |
| Progestin Only Birth Control Pills | 1.0 | 2.5 |
| Condom and Foam | 1.0 | 2 |
| IUD | 1.5 | 4 |
| Condom | 2 | 10 |
| Diaphragm and Jelly | 2 | 10 |
| Cervical Cap | 2 | 13 |
| Foam, Creams, Jellies, Suppositories | 3 - 5 | 15 |
| Mucus Observation | .1 - 5.7 | 2.3 - 39.7 |
| Sympto-thermal Method | .5 - 13.1 | 4.5 - 34.4 |
Source: Contraceptive Techonology, 1982-1983, 11th rev. ed., (New York: Irvington Publishers, 1982), p. 112