The Demographer's Complaint

I have confirmed 'confirmation bias'. It is said that if you look for something long enough, you will find it. I guess the important thing is that you are wise in your choice of searching. So as I predicted, there would be an expert to raise important questions about the science behind the controversial Lancet study of Iraqi deaths. I'm quoting Volokh in toto, it is roughly my opinion:

Daniel Davies is impressed with the Lancet study estimating 655,000 "excess" Iraqi casualties since the U.S.-led invasion.  Based on his experience conducting surveys in Iraq, Steve E. Moore is not.

Of Moore's criticisms, the most significant seem to be 1) the relatively small number of cluster points used for the survey (which, he claims, is more important than the number of actual interviews in the sample); and 2) the failure to obtain demographic data on those interviewed so as to verify the representativeness of the survey sample.

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. . . .

With so few cluster points, it is highly unlikely the Johns Hopkins survey is representative of the population in Iraq. However, there is a definitive method of establishing if it is. Recording the gender, age, education and other demographic characteristics of the respondents allows a researcher to compare his survey results to a known demographic instrument, such as a census. . . .

while the gender and the age of the deceased were recorded in the 2006 Johns Hopkins study, nobody, according to Dr. Roberts, recorded demographic information for the living survey respondents. . . .

Without demographic information to assure a representative sample, there is no way anyone can prove--or disprove--that the Johns Hopkins estimate of Iraqi civilian deaths is accurate.

These are also criticisms that I have not seen responses to elsewhere (e.g. here).  No charges of fraud here, just poor methodology.

I do not mean to diminish the tragedy of civilian Iraqi deaths. I agree with Moore that "there have been far too many deaths in Iraq by anyone's measure," and I certainly believe that the Bush Administration's poor policy decisions and execution bear a significant portion of the blame. Nonetheless, Moore seems to mount a serious challenge to the validity of the Lancet estimates.

And futhermore:

    Curious about the kind of people who would have the chutzpah to claim to a national audience that this kind of research was methodologically sound, I contacted Johns Hopkins University and was referred to Les Roberts, one of the primary authors of the study. Dr. Roberts defended his 47 cluster points, saying that this was standard. I'm not sure whose standards these are.

    Appendix A of the Johns Hopkins survey, for example, cites several other studies of mortality in war zones, and uses the citations to validate the group's use of cluster sampling. One study is by the International Rescue Committee in the Democratic Republic of Congo, which used 750 cluster points. Harvard's School of Public Health, in a 1992 survey of Iraq, used 271 cluster points. Another study in Kosovo cites the use of 50 cluster points, but this was for a population of just 1.6 million, compared to Iraq's 27 million.

    When I pointed out these numbers to Dr. Roberts, he said that the appendices were written by a student and should be ignored. Which led me to wonder what other sections of the survey should be ignored.

    With so few cluster points, it is highly unlikely the Johns Hopkins survey is representative of the population in Iraq. However, there is a definitive method of establishing if it is. Recording the gender, age, education and other demographic characteristics of the respondents allows a researcher to compare his survey results to a known demographic instrument, such as a census.

    Dr. Roberts said that his team's surveyors did not ask demographic questions. I was so surprised to hear this that I emailed him later in the day to ask a second time if his team asked demographic questions and compared the results to the 1997 Iraqi census. Dr. Roberts replied that he had not even looked at the Iraqi census.

    And so, while the gender and the age of the deceased were recorded in the 2006 Johns Hopkins study, nobody, according to Dr. Roberts, recorded demographic information for the living survey respondents. This would be the first survey I have looked at in my 15 years of looking that did not ask demographic questions of its respondents. But don't take my word for it--try using Google to find a survey that does not ask demographic questions.

    

BAM!