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In one of the most highly publicised statements, in October 2003, the President of the Vatican's Pontifical Council for the Family, Cardinal Alfonso Lopez Trujillo, said: "The AIDS virus is roughly 450 times smaller than the spermatozoon.
The spermatozoon can easily pass through the 'net' that is formed by the condom.
Another kind of study is to conduct a prospective cohort study, looking at differences in HIV incidence between two groups of people according to their usage of condoms.
This cannot be a randomised controlled study, but participants’ HIV and STI incidence can be related to their condom use either at baseline or preferably (because behaviours change over time) by means of regular questionnaires and monitoring.
These can be done in individuals whose characteristics are known and can be controlled for, and if the relationship truly is monogamous then infections by acute STIs and from outsiders can be ruled out.
One disadvantage is that condom use in long-term relationships, even in serodiscordant couples, is relatively rare.
(See the text of Museveni’s speech.) Museveni later complained of being misunderstood and signed an article in The Lancet saying that condoms formed a valuable part of HIV prevention.The next problem is deciding what kind of study provides truly reliable evidence.It would be unethical to mount a randomised trial of condom use because the control group would have to stop using them altogether.The main findings of studies we look at in more detail below are as follows: These degrees of protection may be lower than some readers expect, and rates of 98% reliability are still sometimes quoted for condoms.These are based upon observations of their use in contraception: studies have shown that 98% of women relying on condoms as their sole form of contraception remain pregnancy free if condoms are used perfectly, meaning that they are used consistently and correctly at every act of sexual intercourse.