Over half a million additional deaths in Iraq since US invasion
A new study by American and Iraqi epidemiologists estimates that there have been 665,000 excess deaths in Iraq since the U.S. invasion of 2003. This study, published in the Lancet, is the best scientific estimate of deaths attributable to the invasion. All other methods for estimating the number of deaths pale beside a population based study.
Instead of extrapolating the death toll from police reports or media coverage, Iraqi scientists fanned out over the country and asked Iraqis how many members of their households had died since 2003.
Public health scientist Cervantes explains the methodology behind the Lancet study. As he notes, the scientists observed standard protocols for investigating questions of this type:
So, the researchers set out to estimate deaths by means of a household survey using area probability sampling methods. This is a method used all the time in health surveys. It's a method I have used myself, in fact. To begin, you just need census data -- it actually doesn't even have to be highly accurate as long as any errors are essentially random, or unrelated to your study questions. Then, you pick geographic areas based on probability proportionate to the population they contain. This is usually done in stages. In the Iraq study, they first determined the number of clusters they would select in each province based on population size (Baghdad, with its population of over 6 million, got 12; Muthanna, with a population of 570,000, happened to get none.) Then, towns, blocks, and starting households were selected at random. For each household selected, the 39 nearest houses were also included. This survey had a total of 47 clusters, including 12,801 persons.
The researchers interiewed adult household members between May and June, 2006, to learn about births, deaths, and migration since January 1, 2002. They also asked people to report if an entire neighboring household had been wiped out, to account for households with no-one left to speak for them. They report that for 92% of reported deaths, the respondents were able to produce a death certificate. A substantial omission in the report, I must say, is the failure to state the response rate. The investigators also refer to procedures for substituting areas which were too unsafe to visit. They do not say how often this happened, but if anything, it would tend to bias the results downward.
To arrive at an estimate of total deaths for the country, they simply multiply the deaths in the study population by the appopriate weights for the number of people each cluster represents (i.e., the inverse of the probability that a person living in that province would have been selected). The clustering does not directly affect the estimates, but it does affect the so-called confidence interval. Since people living in a specific area are at greater or lesser risk of violent death than average, the statistical power of the study is less than it would be for a single stage probability sample of 12,801 persons, because of the possibility that the selection of clusters introduced sampling error. Although the manuscript does not discuss the specific calculations that were done to adjust for this, I am willing to give investigators from these institutions the benefit of the doubt that they did it correctly.
To recap: The investigators conducted interviews in 14 of Iraq's 16 districts. Regions were assigned interview sites (clusters) according to their populations. Households within each cluster were selected at random.
Why did the epidemiologists use the cluster technique of a purely random sample? It would have been impractical to conduct a truly random survey in a country the size of Iraq. Instead, the investigators decided how many clusters they were going to have in each region and then picked people at random within their zones. If one person was selected at random, the investigators interviewed all his neighbors to complete the cluster.
The investigators interviewed about 12,800 people out of a population of nearly 30 million. So, of course the 655,000 figure is an estimate. The fundamental question is whether one can meaningfully extrapolate excess death rates for the entire country based on a sample of 12,800. Based on the numbers they observed and the statistical limitations of their methods, the authors estimate that the true number of excess deaths would fall between 426,369 and 793,663 nineteen times out of twenty.
This study estimates the number of excess deaths since the invasion. The investigators compared the death rate shortly before the invasion to the death rate for the years following. The 665,000 is the number of deaths over and above what would have occurred if the pre-invasion death rate held steady over that three-year period.
Of course, there's every reason to believe that the vast majority of deaths go unrreported by the press. After all, most of the country is off-limits to journalists. The authorities who run the morgues keep journalists out, except by special invitation. Thousands of unidentified bodies are being pulled from the Tigris alone.
The the main critique of the study in the right wing blogosphere can be summarized as follows: But 665,000 is a lot!
The right wing Rick Moran shows off his math skills:
Someone is wildly off base here. Could it be the group that says that the US military has killed 180,000 Iraqis as a direct result of military actions?
Gunshot wounds caused 56 percent of violent deaths, with car bombs and other explosions causing 14 percent, according to the survey results. Of the violent deaths that occurred after the invasion, 31 percent were caused by coalition forces or airstrikes, the respondents said.
The fact that those three percentages totalled up equal 101% isn’t as ridiculous as 31% of deaths were caused by coalition forces or airstrikes. [Emphasis added]
The right wing blogosphere is already whining about how there's uncertainty in this estimate. Well of course there is! It doesn't change the fact that this is the best scientific estimate of the number of excess deaths in Iraq since the invasion. Rick Moran and his buddies are now praising Iraq Body Count to the skies. IBC uses media reports to estimate casualties. As admirable as this effort is, it's no substitute for going out and surveying people directly.
We can expect a bumper crop of straw men in the right wing blogosphere. Some wingnuts are complaining that the authors didn't differentiate between civilians, military personnel, and police. No, they didn't. But you see, they didn't claim to, either. The investigators just wanted to estimate how many Iraqis have died since the invasion and compare that number to what we would have expected to see if pre-invasion death rates had continued. I know it's hard for right wingers to wrap their heads around this but: all those dead people were people. Scientists don't keep separate sets of books for the "good guys" and the "bad guys."
Then there's the correlation/causation thing. The wingnuts will emphasize that just because the death rate shot up dramatically after the US invaded doesn't mean that the US invasion actually caused all those extra deaths. No, it doesn't. However, I'll be curious to see what alternative hypotheses they have for the soaring death rate after the invasion. Global warming? Bird flu? Sun spots?
Glenn Greenwald has more.