Now, wiriting in The Lancet, Dr. De Cock has corrected the correction, with the help of Paul Delay at UNAIDS. The facts are the same as those he gave in the original story. But they are hedged about with just enough “yes, buts…” to make them politically correct, too.

Now, guess what? Australian researchers have gone and done the study. With results I wouldn’t have expected.

The passage in The Wisdom of Whores read:

In the first lecture, we ”reviewed” all the major study types. For example the case-control study, where you find a group of people with a disease, and then look for people who are much the same but without the disease. You compare the two groups to see if they have different risks. It’s a relatively cheap method, but it doesn’t tell you much about the order in which things happen. I can’t remember all the examples used in the lecture, but let’s say you want to look at causes of depression in women. You start with 600 depressed women, find another 600 who match them on age, ethnicity and educational status, and then ask them all about their lives. Let’s say you find out that women who are depressed are six times more likely not to have had sex in the last year as women who are cheerful. That means if you’re not having sex you get depressed, right? But hang on, couldn’t it be that women who are moping around looking miserable don’t get laid much?

Perhaps you’d be better off with a cohort study. You start off with several thousand women who are perfectly happy. Then you follow them over time, recording their behaviours, and see which of them get depressed. If you find that women who have sex are less likely to become depressed than women who aren’t getting any, it suggests it is the lack of sex that causes the depression, not the depression which stops you getting laid. You can throw out the “misery guts” theory and recommend more good sex as an intervention to promote mental health.

The Australian research, led by Sabura Allen, isn’t published in full yet. But according to an AAP report, they found that depressed women have more sex than happy women, at least in Melbourne where the study was conducted. I’m looking forward to seeing the full paper. But I’d be prepared to bet that these results come from a cross-sectional study, not one that follows women over time. If I’m right, we’re still left with the question, which come first, the depression or the sex?

As Melbourne stalwarts Rob Moodie and Gabriel Gate say in their wonderful new book “Recipes for a Great Life”, “We want to be held,kissed, caressed. It’s why we seek relationships”. To this extent, they seem to agree with Allen, who advances the theory that women who are a bit miserable go looking for sex because it makes them feel better. But the Melbourne Life Cooks recipe for better sex? “Have Fun”. Which leaves me with an alternative hypothesis about the link between sex and sadness for women. Perhaps they’re not having fun. Perhaps men in Melbourne are just not very good at sex. That would be depressing…

Voting is like sex. It is something that (usually!) happens in private. People have no incentive to tell nosy researchers the truth about what they have just done. Oddly, though, people don’t lie very much about either sex or voting, as long as you ask about a specific, recent event. The exit polls in New Hampshire stacked up nicely against reality. In the same way, studies that have collected used condoms from brothels have found that both sex workers and clients report condom use at last sex fairly accurately. The lying comes in when you ask people what they intend to do. Most people say they intend to “do the right thing”, to use condoms when they next have sex with a casual partner, for example. But when things hot up, condom use slips. The “right thing” gets overtaken by the comfortable thing.

Apparently, a lot of people intended to vote for Barack Obama. Their behaviour didn’t match their intentions. That doesn’t mean they were lying. But it does give pause for thought about what is right and what is comfortable for Democratic voters in the US.

“There may be a negative one” she reasons. “Success at work may go hand in hand with failure in matirmony. Successful people have bigger egos, are in the office all the time, have lots of money and the opportunity to stray.” In other words, Kellaway implies, the character traits and circumstances that make you successful and the trappings of success combine to undermine the prospect of a successful marriage. Thus spake the management guru.

But let’s look at the same question through an epidemiologist’s glasses (rephrasing it as a pedantic epidemiologists would have to): “is there any correlation between between good marriages and good work relationships?” We’d collect data from the 3,000 couples in the “Love Labs” Kellaway refers to. We’d ask them endless questions about their marriage and their working relationships, how much time the spend at work and at home, how much money they spend on husbands and toy boys. If we had a generous enough grant, we’d ask their husbands and their colleagues too. We’d devise a five-point scale to measure ego and satsifaction in the bedroom and the boardroom. We’d spend six months on the analysis, and two months writing it up for publication. And we may well conclude that there is a negative correlation between good marriages and good work relationships, because successful people have bigger egos, are in the office all the time, have lots of money and the opportunity to stray.

Then, in the discussion section of our paper, we’d point out that we can’t, in a cross-sectional study, ascertain the direction of causality. Perhaps people are in the office more because they have bad marriages? Perhaps they score well on relations with their colleagues because they are as good in the bedroom as the boardroom, and, denied the chance to practice in their bad marriage, are generously sharing their skills with their staff? So maybe it is not success in business that undermines a good marriage, but failure in marriage that fertilises success in business.

Kellaway dismisses one of the Love Lab’s key findings, that contempt doesn’t do much for marital happiness: “you don’t need to have observed 3,000 marriages to work that out.” But we epidemiologists would draw a different conclusion. This cross-sectional study points to important and sometimes unexpected correlations between success at home and at work. A longitudinal cohort study is needed to ascertain the direction of causality in the relationship.” Surely worth another grant proposal…

Let’s be clear — the lower figures in India are the result of better data, not good prevention programmes. They represent a triumph of surveillance and spreadsheets, not a triumph of clean needles and condoms. Essentially, India has been looking for its epidemic in all the wrong places. Against the advice of just about everybody, including some of its own top public health officials, the Indian government has for years stuck stubbornly to an HIV surveillance system which is entirely inappropriate to its epidemic. It has been measuring infection rates in pregnant women and STI patients rather than in the sub-populations most likely to be infected: drug injectors, sex workers, their clients, and men who have anal sex with one another.

It has taken a hugely expensive survey of over 102,000 households to get closer to the truth. What the Dandona’s don’t mention is that the bare bones of a more sensible surveillance system focusing on high risk populations has been built up over the past two years by the Avahan project, with funding from the Bill and Melinda Gates Foundation. This has provided a much more detailed picture than was previously available of levels of HIV infection and risk behaviour in those most likely to be exposed to the virus, but it only covers a handful of states. India would do well to expand these efforts. This would allow the country to keep better track of its epidemic, and, most importantly of all, to do a better job of providing HIV prevention services to the people who need them most, rather than scattering its efforts across populations who were never at any great risk of infection in the first place.

He points out several situations where HIV prevalence could be expected to rise, for “good” reasons. Obviously, the longer people survive with HIV, the more people there will be living with HIV at any one time. So yes, increased access to life-prolonging medicine can be expected to result in a rise in HIV prevalence. Does that mean lower prevalence is a “bad” thing? Not necessarily.

The cries of victory from Zimbabwe are based on prevalence rates among pregnant women aged 15-24. HIV prevalence among women in this age group has fallen by more than a quarter in urban areas from 2000 to 2006. Rates seem to have drifted downwards in rural areas too, but not significantly. Could this be, as Tim posits, because more people are dying more quickly? It is possible, of course, but by restricting the analysis to women under 25 the chances of that are limited. Even in rural areas with exceptionally limited health services, people with HIV live a median of between nine and ten years. You’d have to have a truly massive deterioration in general health to see much of an impact of reduced survival in people under 25.

Tim speculates that lower prevalence may be the result of outmigration. But this only works if there is a selective outmigration of HIV-infected people (and in this case a selective outmigration of HIV-infected women aged 15-24, which seems unlikely).

Could prevalence be falling because there are fewer new infections? In other words because HIV negative people are actually less likely than before to be having unprotected sex with someone who is already infected, and who is highly infectious? Possibly. People could be having no sex at all, or no unprotected sex at all, but that wouldn’t account for any changes we see among pregnant women, because they have by definition had unprotected sex.

Could young women be less likely to be having sex with someone infected? Yes, for example if young girls drop their sugar daddys in favour of sex with boys their own age or younger, since those boys are far less likely to be infected than the older men who can provide nice meals, visits to nightclub and units for the cellphone, as well as HIV infection. Could new infections be falling because young women are less likely to be having sex with someone infectious? Yes, if access to antiretorvirals is expanding and adherence is good, because good treatment regimes lower viral load, and that lowers infectivity in the positive partner.

If new infections are falling because uninfected people are less likely to be having sex with infectious people, it still begs the question: is that the result of prevention programmes, or of other factors such as a “personal witness” effect, as Tim suggests? I think the question is a somewhat spurious — it’s just not possible to disentangle the effects. But lets look for a moment at “personal witness”.

Do people change their sexual behaviour if they see a lot of people around them dying of AIDS, which they know is the result of a sexually transmitted virus? It is very plausible. It seems to have happened among gay men in rich countries, and among men and women in Uganda. Do people change their sexual behaviour if they see a lot of people around them dying, but believe the deaths are the result of poverty, witchcraft, post-colonial malevolence or any of the other things that have been hinted at as causes of AIDS, things that allow people not to think about sex? That seems less plausible. I don’t know what proportion of AIDS-related deaths in Zimbabwe have been recognised as being the result of people’s sexual choices and behaviours, but if the proportion is small (as it is in neighbouring South Africa, for example), the witness effect is unlikely to be large.

My own suspicion is that lower prevalence in Zimbabwe is indeed the result of the country’s economic implosion. Not because of outmigration or reduced survival, but because men can no longer afford to support several women, and older men can no longer afford to buy the things that younger women want in exchange for sexual favours. I’m not the only one who thinks this. Craig Timberg wrote a nice story about it in the Washington Post some months ago.

One in 30 adults in Washington DC is infected with HIV, and that’s just the people we know about. That puts the capital of the United States on a par with Congo, Ethiopia and Angola.

Why these scandalously high rates, over 9 times the national average? The report (pdf file, 139 pages) from the Washington DC Department of Health doesn’t say. But here’s one guess: Federal funds can’t be used to pay for programmes that help drug injectors to shoot up more safely (even though all the major federally funded scientific institutions say these programmes save money as well as lives). For over 200 cities in the country, the restriction has been annoying, but not fatal. They’ve spent state or city funds on making sure injectors have easy access to sterile needles and syringes, in programmes that also refer drug users to detox services. Poor old DC is hamstrung by the need to get Congress to approve its spending, and Congress has forbidden DC to provide safe injecting programmes for nearly a decade. So injectors share needles, their sex partners get infected, and Washington glories in HIV infection rates that are higher than those of Angola, Ethiopia, Congo or Rwanda.