Monday, October 23, 2006

Number Crunching

Number Crunching - By Fred Kaplan - Slate Magazine: "Let's say that the study is way off, off by a factor of 10 or five—in other words, that the right number isn't 655,000 but something between 65,500 and 131,000.

The researchers reached this conclusion through a common technique known as "cluster sampling." They randomly selected 47 neighborhoods in 18 of Iraq's regions. Within those neighborhoods, they visited a total of 1,849 households, comprising 12,801 residents, and asked how many of their members had died before the invasion and since the invasion. The researchers then extrapolated from this sample to the entire Iraqi population of 27 million people—from which they concluded that since the war there have been about 655,000 "excess deaths," of which 601,000 were caused by violence.

Based on the household surveys, the report estimates that, just before the war, Iraq's mortality rate was 5.5 per 1,000. (That is, for every 1,000 people, 5.5 die each year.) The results also show that, in the three and a half years since the war began, this rate has shot up to 13.3 per 1,000. So, the "excess deaths" amount to 7.8 (13.3 minus 5.5) per 1,000. They extrapolate from this figure to reach their estimate of 655,000 deaths.

However, according to data from the United Nations, based on surveys taken at the time, Iraq's preinvasion mortality rate was 10 per 1,000. The difference between 13.3 and 10.0 is only 3.3, less than half of 7.8. "

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