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Monday, June 06, 2005

Lancet's 100,000 Deaths in Iraq Vindicated? Nope.


Before the presidential election, the medical journal Lancet released a study finding 100,000 excess deaths from the Iraq war. Since then, the UN and the Iraqi government have released a new study (the ILCS survey) with a much larger sample size, finding about 24,000 deaths from military action. This has lead to much uninformed crowing from the right, charging that the Lancet study has been refuted.

The fact is, the two numbers are not comparable. The Lancet figure is for all excess deaths, and is based on higher post-war rates of violent crime, disease, infant mortality, and so on. The ILCS figures ask specifically about deaths due to combat.

But now Tim Lambert, an Australian computer science professor who delights in denouncing bad science and has written over 40 blog entries defending the Lancet study, has done some new calculations based on the Lancet data. And he's crowing that the Lancet study has been "vindicated."

Lambert calculates that 33,000 deaths occured as a direct result of fighting in Iraq. Since the Lancet study is for a slightly longer period (18 months vs. about 14 months), Lambert concludes that the numbers suggest about the same death rate. But Lambert's claim of "vindication" is just as flawed as the earlier right-wing debunking.

First, the ILCS counts include Iraqi soldiers killed during the war, while the Lancet counts include only civilians: so say the authors of the two studies. More importantly, Lambert's figures exclude Falluja, where most of the deaths in the Lancet sample occured. If Falluja were included, the Lancet figure would be 189,000, almost an order of magnitude higher than the ILCS numbers.

Now, I don't deny that there are good reasons to exclude the Falluja cluster. But if you do so, you can't claim to have an estimate of war-related deaths in Iraq. You have an estimate of war-related deaths in areas without intense combat. In a letter to the editor of a British newspaper, the Lancet authors give a good description of the issue.
Our study found that violence was widespread and up 58-fold after the invasion; that from 32 of the neighbourhoods [i.e. excluding Falluja] we visited we estimated 98,000 excess deaths; and that from the sample of the most war-torn communities represented by 30 households in Fallujah more people had probably died than in all of the rest of the country combined.

Fallujah is the only insight into those cities experiencing extreme violence (ie Ramadi, Tallafar, Fallujah, Najaf); all the others were passed over in our sample by random chance. If the Fallujah duster is representative, there were about 200,000 excess deaths above the 98,000.

Perhaps Fallujah is so unique that it represents only Fallujah, implying that it represents only 50-70,000 additional deaths. There is a tiny chance that the neighborhood we visited in Fallujah was worse than the average experience, and only corresponds with a couple of tens of thousands of deaths. We also explain why, given study limitations, our estimate is likely to be low.
I hope I'm not belaboring this obvious point: excluding the part of the sample where the most war-related deaths occured means that the Lancet's 100,000 and Lambert's 33,000 are likely to be underestimates. Indeed, in other contexts the Lancet's defenders on the web have emphasized this point: the Lancet figures are conservative, probably very conservative. Lambert himself has written that "excluding Falluja biases the results downwards."

Now Lambert appears to have changed his mind. I've raised this point with him on his blog, and as near as I can figure out, his reply is that Falluja was uniquely violent, or that the period covered by the Lancet survey after the ILCS survey had ended (April or May 2004 to September 2004) was uniquely violent. So he claims that the figures from the two surveys are comparable even when the Falluja data is dropped from the Lancet survey.

In fact, both surveys cover time periods with similar amounts of fighting. Both surveys exclude the second round of fighting in Falluja during November 2004. Both surveys include the intense fighting during the conventional war itself (March-April 2003). In general, there has been a lot of fighting in Iraq, at many times and places.

According to the Iraq Body Count, 7,981 civilians were killed from the start of the war until March 2004, a time period covered by both surveys. During intense fighting in Baghdad, Falluja, and other parts of Iraq in April 2004, another 1,165 civilians were killed. These deaths are covered in the Lancet survey, but some were probably missed by the ILCS, which was in the field from March 22, 2004 to May 2004. Finally, 1,696 civilians were killed in fighting from May 2004 to September 2004, a time covered only by the Lancet study. The Iraq Body Count figures are based on newspaper reports, and so probably miss many deaths. But there's no reason to doubt that they get the time pattern of deaths about right.

Some calculation shows that the ILCS survey covers about 3/4 as long a time period as the Lancet study, during which time about 3/4 of the deaths occured. Although there was a lot of fighting in April 2004, the next 3 or 4 months were relatively quiet. So Lambert's claim that "the intense fighting was mostly after the ILCS was conducted" is simply false.

And that leaves us back where we started. Lambert's 33,000 figure of war-related deaths in a narrow population (excluding areas of intense combat and the deaths of soldiers) just isn't comparable to the ILCS figure of 24,000 for the whole population. If anything, the similarity of these numbers suggests that something went very wrong with the Lancet study. It certainly doesn't "vindicate" it.

[The Iraq Body Count figures can be found here (for the first 50 days of the war) and here (for the period since then)].
 
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