Published online 12 November 2008 | Nature | doi:10.1038/news.2008.1223

News: Q&A

Calculating the death toll from the crisis in the Democratic Republic of the Congo.

Richard Brennan, the IRC's health director. IRC

Conflict once again rages in the Democratic Republic of the Congo (DRC). A figure often quoted is that 5.4 million people have died from the war there since 1998, making it the deadliest crisis since the Second World War. Nature News spoke to Richard Brennan, health director of the International Rescue Committee, a relief charity with its headquarters in New York. Brennan is one of the researchers behind the survey that produced this number.

When we say 5.4 million, is that people who have died in fighting?

The vast majority of deaths are not from violent injury. The vast majority of deaths, over 90%, are due to common infectious diseases, malnutrition; the fact people don't have access to health care, and so on.

How did you calculate that figure?

It's not possible to do a simple, random-sample survey in a country like the DRC. What pollsters do is they get the telephone book and they pick people at random, essentially. That gives them a pretty even distribution across the country.

It's clearly not possible to do to that in a country like Congo. What you have to do is randomly select health zones around the country, based on proportion of population size. So a health zone with a population of 200,000 will have twice the chance of being selected as a health zone with a population of 100,000.

We selected 35 health zones that way in our last survey. Then we actually went to the health zone itself and asked for a breakdown of all the villages and their populations. We selected 20 of those randomly, again proportionate to the size of population.

Next, we went out to the village with the assistance of local health-authority staff who speak the language. We would select 20 households at random, then go and ask them a series of questions about the people living in the house: their age, their sex, the number of deaths, what people died from, and so on.

How did collecting the data actually work on the ground?

Logistically, it's a very difficult country to get around. It's the size of Western Europe with only about 2,000 kilometres of paved roads. Often, that would mean we'd have to charter an aeroplane or ride motorbikes — maybe we'd have to paddle a canoe, rent a boat, hike up mountains. It could take two days to get to a village.

How reliable is your figure of 5.4 million deaths?

In our most recent survey, there were only about 160,000 people we didn't get access to. The vast majority of the country was open to surveying. We're pretty confident we've got a representative sample of the population.

“Everyone focuses on the figure of 5.4 million. What's more important is the rate at which people are dying.” Richard Brennan

International Rescue Committee

I could go on for some time talking about the limitations and caveats of the data, but it's like any survey: you take a sample, you make some assumptions and extrapolations and you make your best estimates based on that.

Everyone focuses on the figure of 5.4 million. What's more important is the rate at which people are dying, and our surveys estimate this. We then extrapolate this to determine how many people died in excess of what you would have expected over that period of time. That requires a little more art than just pure science, but we always feel the assumptions and extrapolations that we make have been conservative in nature. That's why we have stood by the figures we've come up with.

So how high above expectations was the rate of deaths in the DRC?

There's a little controversy about that, because we don't have absolute baseline data for the period before the survey. A census done in 1984 indicated that the mortality rate across the country at that time was 1.3 deaths per 1,000 per month. The average for sub-Saharan Africa is 1.4 to 1.5 deaths per 1,000 per month.

Across the DRC this time, we found a death rate of 2.2 deaths per 1,000 per month. That's clearly significantly higher than the average for sub-Saharan Africa or that reported for the country as a whole in 1984.

Other mortality figures in areas of conflict, especially those that have come out of Iraq, have been hugely controversial. Does politics start to enter into those discussions?

There's no question that politics comes into it. People can disagree about the assumptions and extrapolations that you make as well. Some people question our assumptions, although most people accept what we have done. I've got colleagues who say we should have used a baseline of 2.0 [deaths per 1,000 per month], but based on what?

Are any of your team still in the DRC?

Yes. We've got a large health programme there. We've been working in Rutshuru district, which is one of the worst affected areas. We've had to evacuate our team because several of our staff were roughed up out there. As soon as the security situation allows, we will be expanding our programmes. Right now, we're providing water and sanitation services and some basic medical care.

How might the death toll change as a result of the current situation?

I think there's every reason to expect that in the area that's been impacted by the conflict, in north Kivu, the mortality rates will go up. Again, most of them won't be a result of violent injury. Most of them will be caused by the indirect consequences of conflict — increased rates of infectious disease, malnutrition.