No one disputes that Iraq has grown much more deadly. The question is how much.
A 2004 study by the same authors of the Lancet article estimated 98,000 violent deaths in the first 18 months after the invasion, a figure four times higher than the findings of a much larger survey done at approximately the same time by Norweigan researchers working for the United Nations. That study, the Iraqi Living Conditions Survey, estimated 23,743 civilian deaths in the first 13 months of the conflict.
In a telephone interview, Jon Pedersen, research director for the 2004 study, said several factors probably account for researchers' different findings.
One key issue is how researchers extrapolate from the deaths identified in their field research to a death toll for the whole country. Pedersen noted that the Lancet study is based on a pre-invasion mortality rate of 5.5 deaths per thousand people. The U.N., he said, used the figure of 9 deaths per thousand. Extrapolating from the lower pre-invasion mortality rate would yield a greater increase in post-invasion deaths, he noted. If the higher pre-invasion mortality rate is more accurate, then the deaths attributable to the war would be lower.
Another difficulty, he said, is doing accurate research under dangerous conditions. Pedersen wondered how tightly the study's authors could oversee the interviews as they were conducted throughout Iraq.
The JHU study, he noted, asked Iraqis only about mortality. The U.N. study asked Iraqis about many aspects of their living conditions. Pedersen said his study probably underestimated deaths caused by the war because the interviews did not focus on the issue, while the Lancet article probably overstated them because no other subject was discussed.
Pedersen said he thinks the Lancet numbers are "high, and probably way too high. I would accept something in the vicinity of 100,000 but 600,000 is too much."
"Regardless of the numbers that are possible," he added, "we are seeing a situation that is pretty horrible."
Agreed. But, if Pedersen is correct, how did Lancet II come up with a number 6 times greater than the truth? Was there a problem in their statistical software? Did they make a mistake in some arcane cluster sampling calculation? Unlikely. The most likely source of error, as I have said for many months, is the raw data. Are all the supporters of Lancet II 100% convinced that Pedersen is wrong?
It seems to me that the truth is most likely to lie somewhere between Lancet II's estimate and Pedersen's.