I have heard numbers that state some condoms are 97 percent effective, or
95 percent effective. Anyone know exactly what this means? To what period
does this apply? Or does it apply to one or more uses?
I know what it means, but it is somewhat involved, and the numbers are questionable. Where did you get them? You should cross-check them with several different authoritative sources. Anyway, here is an over-simplified explanation:
Condoms serve two purposes: 1. Contraception, and 2. Preventing sexually transmitted diseases (STD). The latter is much more difficult; a condom might succeed in 1 but fail in 2. This is particularly likely if it is only used in the last stages of intercourse.
Failure is mainly mechanical: the condom rips or falls off during intercourse. Modern condoms very seldom have pinhole leaks weak seams or other manufacturing defects. The likelihood of failure depends mainly on the user. People who can read and understand instructions seldom have a problem, but unfortunately many users are Third World illiterates. Education can greatly reduce the failure rate. Also there are some advanced designs that incorporate spermicides, virucides and other drugs in the condom, and this enhances effectiveness for both 1 and 2 even in the event of a mechanical faillure. Unfortunately, these are expensive and not widely used in the Third World.
When failure is expressed as a percent, you have to be very careful to define your terms. I assume that the term "95% effective" means that 5% fail mechanically. I doubt the number is this high, but I have no data, and I think it would be very difficult to collect reliable data. Patients do not want to talk about this! Numbers like "95 or 97%" sound very fishy to me because you can never establish the sort of thing to within 1%. Even if 5% do fail, that does not mean there is one chance in 20 the woman will become pregnant. At the peak of fertility, a woman has only roughly a 1% chance of becoming pregnant, so if 5% of condoms fail, and a couple always uses one during every phase of intercourse, they have roughly a 0.05% chance of pregnancy from that failure, which is tantamount to zero. It is nothing to worry about. If every couple in a society uses them consistently, the birthrate will instantly drop close to zero. In other words, even though individuals run a small risk when they use condoms, as a means of controlling the overall population there are no risks at all. Actually, the same can be said for the so-called "rhythm method." It is about as safe as Russian Roulette for the individual women who practice it, but for society as a whole it will drastically reduce population growth.
As for STD, condoms when used correctly are extremely effective against most, but not so effective against others. I think that against AIDS they have a somewhat mixed record, but again this is comparable to the "rhythm method." If everyone in a society uses condoms, the spread of AIDS will be stopped instantly, and eventually the disease will go extinct because I do not think it survives outside the human body. (In other words, it is like smallpox or polio -- it requires a human host.) However, during the period AIDS is being driven to extinction by the use of condoms, individual condoms will still fail and some people will get the disease. It is not like a vaccination, which works for nearly everyone without fail.
Bear in mind that an STD does not automatically or invariably transmit during unprotected sex or after a condom fails, so again, even if the failure rate is 5%, that does not mean you have one chance in 20 of getting AIDS with an infected partner. Also, the rate of infections for many STD (including AIDS) from male to female is considerably higher than from female to male. It is very complicated and you cannot summarize it in a meaningful way with a single number such as "5%."
- Jed
