Steven E. Moore discovered a fatal flaw in the recent John Hopkins report on Iraqi casualties and published his findings in today’s WSJ:

The group–associated with the Johns Hopkins Bloomberg School of Public Health–employed cluster sampling for in-person interviews, which is the methodology that I and most researchers use in developing countries. Here, in the U.S., opinion surveys often use telephone polls, selecting individuals at random. But for a country lacking in telephone penetration, door-to-door interviews are required: Neighborhoods are selected at random, and then individuals are selected at random in “clusters” within each neighborhood for door-to-door interviews. Without cluster sampling, the expense and time associated with travel would make in-person interviewing virtually impossible. However, the key to the validity of cluster sampling is to use enough cluster points. In their 2006 report, “Mortality after the 2003 invasion of Iraq: a cross-sectional sample survey,” the Johns Hopkins team says it used 47 cluster points for their sample of 1,849 interviews. This is astonishing: I wouldn’t survey a junior high school, no less an entire country, using only 47 cluster points. Neither would anyone else. For its 2004 survey of Iraq, the United Nations Development Program (UNDP) used 2,200 cluster points of 10 interviews each for a total sample of 21,688. True, interviews are expensive and not everyone has the U.N.’s bank account. However, even for a similarly sized sample, that is an extraordinarily small number of cluster points. A 2005 survey conducted by ABC News, Time magazine, the BBC, NHK and Der Spiegel used 135 cluster points with a sample size of 1,711–almost three times that of the Johns Hopkins team for 93% of the sample size. What happens when you don’t use enough cluster points in a survey? You get crazy results when compared to a known quantity, or a survey with more cluster points. There was a perfect example of this two years ago. The UNDP’s survey, in April and May 2004, estimated between 18,000 and 29,000 Iraqi civilian deaths due to the war. This survey was conducted four months prior to another, earlier study by the Johns Hopkins team, which used 33 cluster points and estimated between 69,000 and 155,000 civilian deaths–four to five times as high as the UNDP survey, which used 66 times the cluster points. The 2004 survey by the Johns Hopkins group was itself methodologically suspect–and the one they just published even more so.

No big deal. I’m sure Moore’s findings will be just as widely reported as the erroneous results of the study itself.