Iraq Poll: Note on Methodology

ByABC News

March 19, 2007 -- -- 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.

SUNNI/SHIITE (3/22/07) -- Given the attitudinal differences between Shiite and Sunni Arabs in Iraq, there's interest in the relative sizes of these two population groups. As far as we have been able to ascertain there is no official Iraqi estimate of the country's Sunni vs. Shiite Arab populations, and no single authoritative source of empirical data on the subject.

The most commonly cited estimate is an unsourced reference in the CIA World Factbook saying that 60-65 percent of Iraqis are Shiite Muslims, 15-20 percent Kurds and three percent non-Muslims. Though not explicitly stated, that leaves room for 12 to 22 percent Sunni Arabs.

This estimate may be derived from a 1988 book, "Iraq: a Country Study" produced by the Federal Research Division, Library of Congress. This book (pp. 80-81) characterizes data on ethnicity and religious doctrine in Iraq as "not absolutely reliable." It says, "Officially the government sets the number of Shias at 55 percent. In the 1980s knowledgeable observers began to question this figure, regarding it as low. …a more reasonable estimate of their number would seem to be between 60 and 65 percent." It adds, "…the Sunni Arabs…constitute a decided minority of only about 13 percent..." These data also are unsourced. The 60-65 percent Shiite estimate matches that in the CIA World Factbook; the 13 percent Sunni Arab estimate compares to the World Factbook's unstated range of 12 to 22 percent.

Recent survey data, including this poll, have had different results. This survey found 47 percent Shiite Arabs, 35 percent Sunni Arabs, 15 percent Kurds and three percent others.

D3 Systems reports that in its previous surveys it has seen Shiite Arabs in a range from the high 40s to low 50s, and Sunni Arabs in a range from the high 20s to mid-30s. The 35 percent Sunni Arab estimate in this poll is at the high end of its previous data, but within that range. This poll had more sampling points than any previous individual national study in Iraq by D3/KARL.

Other Iraq surveys are difficult to compare because they ask religious doctrine different ways, often reporting significant numbers of Muslims of unspecified doctrine, and use different weights, including, in some cases, weighting to a predetermined assumption of distribution by religious doctrine.

This poll is not weighted to religious doctrine; it's our view that this would be arbitrary and unsupportable in the absence of empirical data establishing appropriate weighting parameters. Experimentally, weighting these results to 30 or even 25 percent Sunni Arab would change numbers on which Sunni Arab and Shiite divisions are greatest, but the average change across all questions would be one or 1.5 percentage points (depending on the weight used), and none of the differences would alter any of the fundamental conclusions in our analysis.

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