Number Crunching

Military analysis.
Oct. 20 2006 6:34 PM

Number Crunching

Taking another look at the Lancet's Iraqstudy.

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The Oxford-Holloway team calls this method "main street bias." They add:

Main street bias inflates casualty rates since conflict events such as car bombs, drive-by shootings, artillery strikes on insurgent positions, and marketplace explosions gravitate toward the same neighborhood types that the [Lancet] researchers surveyed. …

In short, the closer you are to a main road, the more likely you are to die in violent activity. So if researchers only count people living close to a main road, then it comes as no surprise they will over-count the dead.

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Whether or not the Hopkins researchers were aware of this flaw, or its importance, is unclear. An exchange of e-mails with Gilbert Burnham, the study's chief researcher, raises some disturbing questions about this matter. (Click here for the details.)

It's understandable why the surveyors limited their work to the main roads; they were in strange and dangerous places. But that doesn't negate the Oxford-Holloway team's point. By this measure alone, the Lancet study is not a random survey. In statistically proper random surveys, each household has the same probability of being chosen. Yet in the Lancet survey, if a household wasn't on or near a main road, it had zero chance of being chosen. And "cluster samples" cannot be seen as representative of the entire population unless they are chosen randomly.

The Iraq war is a catastrophe in political, military, and—not least—human terms. How much so may be unfathomable as long as the streets of Iraq are still dangerous. In any event, it's a question that the Lancet study doesn't really answer.

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