Iraq Poll: Note on Methodology

March 16, 2009 — -- This survey was conducted for ABC News, the BBC and NHK by D3 Systems of Vienna, Va., and KA Research Ltd. of Istanbul, Turkey. Interviews were conducted in person, in Arabic or Kurdish, among a random national sample of 2,228 Iraqis aged 18 and up from Feb. 17-25, 2009.

Four-hundred-forty-six sampling points were distributed proportionate to population size in each of Iraq's 18 provinces, then in 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. Four sampling points were substituted for security reasons.

Maps or grids were used to select random starting points within each sampling point, with household selection by random route/random interval and within-household selection by the "next-birthday" method. An average of five interviews were conducted per sampling point.

Interviews were conducted by 133 trained Iraqi interviewers with management from 26 supervisors and quality control personnel. Fifty-four percent of the interviews were subject to quality control: Thirty-three percent by direct observation by supervisors and control team members, 11 percent by in-person back-checks by supervisors and 11 percent by regional field managers and central office control staff.

In addition to the national sample, oversamples were drawn in Anbar province, Sadr City, Basra city, Kirkuk city and Mosul 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 93 percent and a cooperation rate of 67 percent for a net response rate of 62 percent. Including an estimated design effect of 1.49, the results have a margin of sampling error of 2.5 percentage points at the 95 percent confidence level.

SUNNI/SHIITE – Given the attitudinal differences between Shiite and Sunni Arabs in Iraq, there's interest in the relative sizes of these two groups. We find no official Iraqi estimate of the country's Sunni vs. Shiite Arab populations and no 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 3 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.

Data from recent random-sample surveys, including the last four sponsored by ABC News with media partners, contrast with these unsourced estimates. This survey puts Iraq's population at 51 percent Shiite, 29 percent Sunni Arab, 16 percent Kurdish and 4 percent other; the four, in aggregate, are 49 percent Shiite, 32 percent Sunni Arab, 16 percent Kurdish and 4 percent other.

These four surveys comprise more than 8,800 interviews from 1,822 sampling points, a large sample with an unusual level of geographical coverage.

Iraq surveys from other sources are difficult to compare, particularly because some weight their results to a predetermined assumption of distribution by religious doctrine. In the absence of persuasive empirical data from any other source, this and previous polls for ABC News and its media partners do not weight Iraqis' religious or ethnic doctrine to any assumed target.