Reliability Of The Major Contraceptives

There are often large discrepancies between different people’s estimations of how effective a particular method is. This can be due to bias — for instance if one person feels that the pill is the easiest and safest method for most women, he or she may well overplay the failure rates of the barrier methods. Also, trials may have been done with women or men who are already fully committed to the method and trained in it, which does not give a fair picture of the average success of the method as used by average ordinary couples. However, there are two generally accepted methods of presenting failure rates, based on clinical trials.

The first is the theoretical failure rate; this is the estimated rate assuming that everyone uses the method consistently and accurately and follows all the related instructions. The second figure is the actual failure rate; this is based on typical users and assumes an element of human error; for instance some people will forget to take a pill, or will decide to take a risk and not use a cap or sheath. Both figures are given as failure rates per hundred woman years (Hwys) — the number of pregnancies that can be expected in a hundred women using the method for the first year.

Obviously some clinics feel that certain figures are more accurate than others; this list is based on the figures of Hatcher et al which is one of the most highly respected annual digests of contraceptive technology.

Theoretical failure rate

Method (or lowest observed rate) – Actual failure rate per HWYS – per HWYS

  • Female sterilization 0.04 0.04
  • Vasectomy 0.15 0.15
  • Injectables 0.25 0.25
  • Combined pill 0.5 2
  • Mini-pill 1 2.5
  • IUD 1.5 4
  • Sheath 2 10
  • Diaphragm plus spermicide 2 10
  • Cervical cap 2 13
  • Spermicide alone 3-5 15
  • Rhythm methods 2-20 20-30
  • No method of contraception 90 90

Unreliable methods

Several of the oldest known methods of contraception are still practised by millions of couples worldwide; these are withdrawal (coitus interruptus), breastfeeding, and douching. Although there is no doubt that among them they have significantly reduced the number of babies produced worldwide, they are unreliable methods for individual couples who are definitely trying not to conceive.