The group essentially repeated the study last year, using a larger sample size. Again, the researchers had interviewers administer what resembled a typical survey of a random sample of households. Appropriately, at the end of the article in the Lancet, the authors discuss issues that may have resulted in a sample that in fact did not meet the "random" threshold.
Problems with interpretation also plagued that second effort. The authors used crude death rates (CDR), which reflect the number of deaths per thousand people, in explaining the rise in mortality. But demographers rarely use CDR, thinking instead in terms of age and sex-specific mortality rates, usually summarized as "life expectancy." That being said, the group reported that the CDR increased from 5.5 per thousand people in 2002 to 13.3 per thousand in the post-invasion period (March 2003 to March 2006).
To put the pre-invasion figure in perspective, consider UN Population Division figures, which are generally considered to be of very high quality. The UN estimates that Iraq's pre-invasion CDR was 10 per thousand, not the 5 per thousand estimated from the two studies. Comparing internationally, the UN reports that Iran's CDR in the 2000-2005 period was 5.3 per thousand. Prior to the war, most observers thought that the situation in Iraq was considerably worse than in Iran.
So the pre-war CDR that the two Lancet studies yield seems too low. It may not be wrong, but the authors should provide a credible explanation of why their pre-war CDR is nearly half that of the UN Population Division. If the pre-war mortality rate was too low and/or if the population estimates were too high -- because, for example, they ignored outflows of refugees from Iraq -- the resulting estimates of the number of Iraqi "excess deaths" would be inflated.
More fundamentally, what purpose do these numbers serve?
Certainly, after the dust has settled, numbers play a role in evaluating the costs and benefits, if any, of a war. But in real time, do the numbers really add to the debate? Do they really provide us with more information than the Iraq Body Count figures provide? Do we have the appropriate context to help us interpret the numbers? The war in Iraq has been exceptionally bloody. For now, that is about all that statistics can safely tell us.
Beth Osborne Daponte is a senior researcher at Yale University's Institute for Social and Policy Studies. Copyright: Project Syndicate