Wednesday, April 04, 2007

ABC Poll Methodology

I haven't had time to review the new ABC poll closely, but their methodology description is commendably thorough.

This survey was conducted for ABC News, USA Today, the BBC and ARD German TV by D3 Systems of Vienna, Va., and KA Research Ltd. of Istanbul. Interviews were conducted in person, in Arabic or Kurdish, among a random national sample of 2,212 Iraqis aged 18 and up from Feb. 25-March 5, 2007.

Four hundred and fifty-eight sampling points were distributed proportionate to population size in each of Iraq's 18 provinces, then in each of the 102 districts within the provinces, then by simple random sampling among Iraq's nearly 11,000 villages or neighborhoods, with urban/rural stratification at each stage.

Maps or grids were used to select random starting points within each sampling point, with household selection by random interval and within-household selection by the "next-birthday" method. An average of five interviews were conducted per sampling point. Three of the 458 sampling points were inaccessible for security reasons and were substituted with randomly selected replacements.

Interviews were conducted by 103 trained Iraqi interviewers with 27 supervisors. Just over half of interviews were back checked by supervisors — 28 percent by direct observation, 14 percent by revisits and 10 percent by phone.

In addition to the national sample, oversamples were drawn in Anbar province, Sadr City, Basra city and Kirkuk city to allow for more reliable analysis in those areas. Population data came from 2005 estimates by the Iraq Ministry of Planning. The sample was weighted by sex, age, education, urban/rural status and population of province.

The survey had a contact rate of 90 percent and a cooperation rate of 62 percent for a net response rate of 56 percent. Including an estimated design effect of 1.51, the results have a margin of sampling error of 2.5 percentage points at the 95 percent confidence level.

Sounds thorough and professional. But then why is the contact rate only 90% (compared to Lancet II's 99%) and the cooperation rate only 62% (compare to Lancet II's 99%)? Isn't it a sign of incompetence on the part of D3/KA that there response rate is more than 40 percentage points lower than that of Lancet II (56% as compared to 98%)?

No, I think that this is evidence that the Lancet interviewers made up data, at least some of it. What other explanation could there be? The D3/KA interviewers were so rude that people didn't want to talk to them? The Lancet interviewers were so charming that virtually everyone was willing to answer their questions?

Other explanations are welcome.


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