Can someone who is intelligent explain this to me

Hey guys, I would have posted this in the sexual health forum, but I still don’t have permission to post there (how many posts does it take?). Anyway, I was reading up the study done in Africa in which they circumcised one group and didn’t circumcise the other and studied the effects on HIV, herpes, and HPV. Here is the link (Male Circumcision for the Prevention of HSV-2 and HPV Infections and Syphilis | NEJM). What I don’t understand is how they get the final statistics from the ones discussed after each STD analysis.

They claim "The cumulative probability of HSV-2 infection during the 24-month period was 7.8% in the intervention group, as compared with 10.3% in the control group," and then, "In the primary intention-to-treat analyses at 24 months, high-risk HPV genotypes were detected in 42 of 233 subjects in the intervention group (18.0%), as compared with 80 of 287 subjects in the control group (27.9%)."

Okay that seems fine, but then in the Discussion they say:
"The efficacies of circumcision for the prevention of HSV-2 incidence and HPV prevalence were 25% and 35%, respectively. Adjustment resulted in a modest increase in efficacy to 28% for HSV-2 infection but did not change efficacy for HPV infection."

The herpes breakdown is the one I don’t understand the most. How did they go from 2.5% higher chance of getting herpes in the analysis to 25% in the discussion?

Thanks
Erock

Well I’m not paying a subscription to argue that one through :)

Oh is that link not the full article or something? It should be free, and it looks complete, but I’m not a real genius when it comes to statistics so maybe I’m missing something.

Erock

Skimmed it on my phone at work but here is a quick thought.. The two numbers represent the infection rate of the whole population the 25% is the change in that ratio. Example. If the infection rate was 10% and something lowered it to 5% that would be a decrease of 50% probability in infection. Or if infection rate was 5% and something made it jump to 10% that would be an increase of 100%. Didn’t read the article and only skimmed the summary but I hope I helped.

That’s gotta be it, thanks a lot slippy!

NJM is free, pf. You sign up for it. But, some of the articles within cost you to peruse and some don’t. However, even if one costs, you get to read the abstract (synopsis) for nothing. Normally with these journals, the abstract will give you a good sense of the whole premise.

Thanks Avocet. I’ll remember that for next time :)

The thing to remember about these studies is that all three of the large Africa trials were cut short of their agreed protocol durations, kind of like gambling on the best two out of three coin tosses but demanding to paid when the first toss comes up heads. It’s no way to run a valid experiment. This magnified two effects:

1) The cut men were abstinent for a long time after their amputations. They couldn’t be contracting HIV sexually during this time, while the men who hadn’t been cut yet were still boning away.

2) HIV and other infections are often not measurable in the blood until months after exposure. So the shorter the study, proportionately the greater the impact of undiagnosed exposures near the end of the observations (when the cut men were finally getting busy again).

Their findings are contradicted by other studies and by common sense. Most of the dead US men who’ve lost the battle with AIDS were circumcised at birth. Europe, where circumcision is rare, has only 1/3 the HIV infection rate we have in the US where like 80% of sexually active males are cut.

Something really stinks about the large Africa trials and I think it’s researcher bias (check the prior writings of Bailey and Halperin). The cut men were exposed over and over to safe sex messages from the friendly white-coated researchers during their treatments and follow-up, and who knows what the intact men were told during that time. Also, EVERY ONE of the subjects sought circumcision, which is to say it had some cultural significance to those men. Perhaps it was seen as a sign of coming of age, of becoming a responsible member of society, or of being a full worthy man in females’ eyes. Perhaps it changed mens’ practices with regard to monogamy or the class of whore they would spring for or the class of tramp they would date.

One other thing, they lost track of many times more men during the study (HIV status unknown) than were infected during the study.

The researchers obviously did not look hard enough at potential confounding factors, because their results just don’t accord with reality.

More recent research shows even if the numbers aren’t cooked, that condoms are 95 times as cost-effective at thwarting HIV in Africa.

The freshly cut African men were found MORE likely to infect their partners with HIV. The African men they cut in these human amputation experiments contracted HIV at a rate 6 times higher than the rate of new infections for African-American men. Hardly a success.