25 percent prevalence among gay men.

Ines So why is prevalence still rising?

In Uganda we see the prevalence went down.

Given the prevalence of bite marks, torn flesh, puncture wounds,

In fact, the HlV prevalence rate is 1.3 percent among adults.

So this is a graph of prevalence estimated by UNAlDS, and prevalence based on the mortality data for the years in the late 1990s in nine countries in Africa.

Because it is true that there was a decline in prevalence in Uganda in the 1990s.

By using this new data, using this information about prevalence over time, we can actually test that.

Unfortunately, there's almost no good data on HlV prevalence in the general population in Africa until about 2003.

So if I asked you, Why don't you go and find me the prevalence in Burkina Faso in 1991?

It's indigenous to China and the Far East, but given that the prevalence of malaria is here in Africa,

Other places have tried things, so why don't we look at those places and see what happened to their prevalence?

But that actually doesn't mean at all that if we gave people more exports, more trade, that that would increase prevalence.

And in fact, if this is the prevalence of the disease, about 100 will have the disease and the rest won't.

The high prevalence of HlV drives researchers to conduct research that is sometimes scientifically acceptable but on many levels ethically questionable.

The reason that we know that the ABC campaign was effective in Uganda is we have good data on prevalence over time.

And I started thinking about how else might we figure out what the prevalence of HlV was in Africa in the past.

So I can tell you what the prevalence was in Kenya in 2003, but I can't tell you anything about 1993 or 1983.

Areas with a lot of economic activity with a lot of roads, with a lot of urbanization those areas have higher prevalence than others.

This shows you in areas with low malaria, medium malaria, high malaria what happens to the number of sexual partners as you increase HlV prevalence.

And so, for a whole host of disorders that occur outside the reproductive tract we see that the incidence or prevalence in men and women can differ dramatically.

I'm here today to talk to you about how volunteerism can be used to reduce the rate of unemployment and the prevalence of crime and poverty within developing countries.

And I think that the answer is, we can look at mortality data, and we can use mortality data to figure out what the prevalence was in the past.

But because people who died this year of AlDS got it a few years ago, we can use this data on mortality to figure out what HlV prevalence was in the past.

You can see that for the prevalence to be as high as UNAlDS says, we have to really see 60 deaths per 10,000 rather than 20 deaths per 10,000 in this age group.

In Nigeria, open source SMS tools are being used by the Red Cross community workers to gather information from the local community in an attempt to better understand and mitigate the prevalence of malaria.

Using a campaign that encouraged people to abstain, be faithful, and use condoms the ABC campaign they decreased their prevalence in the 1990s from about 15 percent to 6 percent over just a few years.

If you look at the blue line, the areas with low levels of malaria, you can see in those areas, actually, the number of sexual partners is decreasing a lot as HlV prevalence goes up.

So it turns out, if you use this technique, actually your estimates of prevalence are very close to what we get from testing random samples in the population, but they're very, very different than what UNAlDS tells us the prevalences are.

So if you combine the intuition in this figure with some of the data that I talked about before, it suggests that somewhere between 25 percent and 50 percent of the decline in prevalence in Uganda actually would have happened even without any education campaign.

And the current state of the art in predicting an epidemic if you're the CDC or some other national body is to sit in the middle where you are and collect data from physicians and laboratories in the field that report the prevalence or the incidence of certain conditions.

And actually, about a year or so ago, there was this promulgation of the idea of Google Flu Trends, with respect to the flu, where by looking at people's searching behavior today, we could know where the flu what the status of the epidemic was today, what's the prevalence of the epidemic today.

Even though it is the case that poverty is linked to AlDS, in the sense that Africa is poor and they have a lot of AlDS, it's not necessarily the case that improving poverty at least in the short run, that improving exports and improving development it's not necessarily the case that that's going to lead to a decline in HlV prevalence.