Contraception is any method that lowers the chance of pregnancy. Hormonal methods use oestrogen and progesterone, or progesterone alone, to stop ovulation or to change the mucus at the cervix so that sperm cannot get through. They include the combined pill, the progesterone-only pill, the contraceptive injection, the skin patch and the implant, which is a small rod placed under the skin of the arm that works for about three years. Barrier methods keep sperm and egg apart. They include the condom and the diaphragm, which is a rubber cap that fits over the cervix.
To evaluate a method, compare how well it works with its drawbacks. No method is perfect. The pill is over 99% effective if taken exactly as directed, but it is less effective in real life because people forget a pill. An implant does not depend on the user remembering anything, so it is very reliable. Hormonal methods can cause side effects such as headaches, mood changes or a small increased risk of blood clots, and they do not protect against sexually transmitted infections.
Condoms have no hormonal side effects and are the only method in this list that also protects against sexually transmitted infections, such as chlamydia and HIV. However, they can split or slip, and then they fail. When you evaluate data, such as the number of pregnancies per 100 women in one year, a lower number means a more effective method.