The skin I live in

What if offering people protection makes take bigger risks?

OK – it has been a worthwhile break. Let’s do this.

Ever since a spate of randomized controlled trials revealed that circumcision can functionally reduce a man’s chance of contracting HIV, global health officials have been been pushing mass circumcision campaigns as much as possible in sub-Saharan Africa. Concerned that the assumption that the internally-valid results from the RCTs may not hold in `the real world’, I wrote a fairly critical post a few years ago. My main concern was that no one was properly accounting for post-treatment behavioural changes.

I was particularly worried about something called the Peltzman effect, a concern that economists have about offsetting behaviour: if you reduce the riskiness of a particular activity for someone, then they have an incentive to do that activity more. While academics have had some trouble reliably identifying Peltzman effects in the real world, it is still a valid concern: while those undergoing an experimental treatment may not change their behaviour before more information on the effectiveness of that treatment is known, men who know that circumcision reduces their chance of contracting HIV might react by simply having more sex.

Someone has finally taken a look at this – Nicholas Wilson, Wentao Xiong and Christine Mattson have a paper specifically looking for the Peltzman effect in a group of Kenyan men who participated in one of these RCTs. They subdivide the sample based on their pre-treatment beliefs on the effectiveness of circumcision, then look at risky sexual behaviour in two follow-ups six and twelve months later. The punchline?

Contrary to the presumption of risk compensation, we find that the response due to the perceived reduction in HIV transmission appears to have been a reduction in risky sexual behavior. We suggest a mechanism for this finding: circumcision reduces fatalism about acquiring HIV and increases the salience of the trade-off between engaging in additional risky behavior and living longer. We also find what appears to be a competing effect that does not operate through the circumcision recipient’s belief about the reduction in the risk of acquiring HIV.

At first glance, this sounds like good news: those who said they believed that circumcision was effective reduced their risky behaviour – the exact opposite of what one would expect from a Peltzman-type relationship. Wilson et al. chalk this up to a sort-of income effect: now that their baseline risk of contracting HIV is lower (therefore raising potential life expectancy), subjects who have been circumcised decide to invest more in life quality, avoiding dangerous behaviours.

But wait – this nugget of good news is actually obscuring something else: those who didn’t believe that circumcision worked increased risky sexual behaviour – they were less likely to use a condom during intercourse and had more sexual partners. The authors don’t have any good explanations for this behaviour, other than suggesting that being circumcised might make men more attractive to other women, since it signals that they have a lower chance of having HIV. I’m not sure how plausible this is, unless men are making their circumcision status public, this is the sort of information that is usually only revealed very, very late in the game. How could we get around this? Randomly reveal men’s circumcision status (sounds fun, but unethical – these two sometimes go hand in hand)?

The increase in risk among the non-believers is disconcerting, even if in net terms there is no increase in risky behaviour. While the believers, who are in the majority, offset the non-believers, we don’t know what the aggregate effects on HIV outside of the sample would be. Nor do we actually see the effects of belief/non-belief on HIV status in this sample, which would be interesting and useful to know:  we could then see to what extent the increase in risky practices offsets the large biological impact of circumcision.

While this is all very interesting, the results of the paper do rely on a strange parsing of the data: reported belief is useful, but might be picking up something else, such as general public health knowledge. Ideally, we’d have some sort of shock to beliefs, say from randomly treating someone to an intensive course on the benefits of circumcision, but perhaps this is asking too much.

What we should be concerned with is what the ratio of believers to non-believers looks like in other settings. The authors specifically recommend that circumcision programmes should come hand-in-hand with information campaigns. If reported belief is something that is malleable, then this is a reasonable strategy. If reported belief is actually a measure of something more inherent, then we’re in trouble.

3 thoughts on “The skin I live in

  1. Mark Lyndon

    January 30, 2012 at 2:49pm

    [I posted this with supporting links, but was told “Hmmm, your comment seems a bit spammy. We’re not real big on spam around here” :-(, so here it is without the links)

    Some very good points.

    “There appears no clear pattern of association between male circumcision and HIV prevalence—in 8 of 18 countries with data, HIV prevalence is lower among circumcised men, while in the remaining 10 countries it is higher.”

    The South African National Communication Survey on HIV/AIDS, 2009 found that 15% of adults across age groups “believe that circumcised men do not need to use condoms”.

    From the committee of the South African Medical Association Human Rights, Law & Ethics Committee :
    “the Committee expressed serious concern that not enough scientifically-based evidence was available to confirm that circumcisions prevented HIV contraction and that the public at large was influenced by incorrect and misrepresented information. The Committee reiterated its view that it did not support circumcision to prevent HIV transmission.”

    The one randomized controlled trial into male-to-female transmission showed a 54% higher rate in the group where the men had been circumcised btw:

    ABC (Abstinence, Being faithful, and especially Condoms) is the way forward. Promoting genital surgery will cost African lives, not save them.

  2. Hugh Young

    January 31, 2012 at 5:46am

    The claim of this clinical trial does not seem to be borne out in the real-world circumcision campaigns. Both men and women are assuming that circumcision is 100% protective and they need not use condoms.

    Since this was done in Kisimu, Kenya you can be reasonably sure that it was in tandem with the circumcising-to-prevent HIV-trial by Bailey, Moses et al, in which 1,393 men were circumcised and 1,391 left intact. After less than two years 47 and 22 men respectively had contracted HIV, 1/3 of the “up to 60% reduction” claim, while 92 and 87 dropped out, their HIV status unknown. So, like that trial, it was geared to promote circumcision, and to “rely on a strange parsing of the data” is par for the course.

    There were only three such trials – hardly “a spate”, and with similar flaws, hardly independent.

  3. aidnography

    January 31, 2012 at 5:08pm

    I just wanted to drop a quick line of ‘welcome back to the aid blogosphere’! And great new stuff is already appearing! T.

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