The Lancet, one of the oldest scientific medical journals in the world, published two peer-reviewed studies on the effect of the 2003 invasion of Iraq and subsequent occupation on the Iraqi mortality rate. The first was published in 2004; the second (by many of the same authors) in 2006. The studies estimate the number of excess deaths caused by the occupation, both direct (combatants plus non-combatants) and indirect (due to increased lawlessness, degraded infrastructure, poor healthcare, etc.).
The first survey . By Les Roberts, Riyadh Lafta, Richard Garfield, Jamal Khudhairi, and Gilbert Burnham. The Lancet, 29 October 2004. There is a version of the PDF article that has a clickable table of contents. It is here: . published on 29 October 2004, estimated 98,000 excess Iraqi deaths (with a range of 8,000 to 194,000, using a 95% confidence interval (CI)) from the 2003 invasion and subsequent occupation of Iraq to that time, or about 50% higher than the death rate prior to the invasion. The authors described this as a conservative estimate, because it excluded the extreme statistical outlier data from Fallujah. If the Fallujah cluster were included, the mortality estimate would increase to 150% over pre-invasion rates (95% CI: 1.6 to 4.2).
The second survey . By Gilbert Burnham, Riyadh Lafta, Shannon Doocy, and Les Roberts. The Lancet, 11 October 2006 . By Gilbert Burnham, Shannon Doocy, Elizabeth Dzeng, Riyadh Lafta, and Les Roberts. A supplement to the October 2006 Lancet study. It is also found here: "Study Claims Iraq's 'Excess' Death Toll Has Reached 655,000". By David Brown. Washington Post. 11 October 2006. published on 11 October 2006, estimated 654,965 excess deaths related to the war, or 2.5% of the population, through the end of June 2006. The new study applied similar methods and involved surveys between 20 May and 10 July 2006. More households were surveyed, allowing for a 95% confidence interval of 392,979 to 942,636 excess Iraqi deaths. 601,027 deaths (range of 426,369 to 793,663 using a 95% confidence interval) were due to violence. 31% (186,318) of those were attributed to the US-led Coalition, 24% (144,246) to others, and 46% (276,472) unknown. The causes of violent deaths were gunshot (56% or 336,575), car bomb (13% or 78,133), other explosion/ordnance (14%), air strike (13% or 78,133), accident (2% or 12,020), and unknown (2%).
The mortality estimates in the Lancet surveys are higher than in several other reports, including those of the Iraqi Health Ministry and the United Nations, as well as other household surveys such as the Iraq Living Conditions Survey and the Iraq Family Health Survey. The 2007 ORB survey of Iraq War casualties estimated more deaths than the Lancet, though it covered a longer period of the conflict."Conflict Deaths in Iraq: A Methodological Critique of the ORB Survey Estimate" By Michael Spagat and Josh Dougherty The Lancet surveys have been supported by some journalists, governments, epidemiologists and statisticians, and been met by criticism and disbelief from other journalists, governments, epidemiologists and statisticians.
First study (2004) The survey was sponsored by the Center for International Emergency Disaster and Refugee Studies, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, United States (authors L Roberts PhD, G Burnham MD) and the Department of Community Medicine, College of Medicine, Al-Mustansiriya University, Baghdad, Iraq. Roberts' team was chosen for their experience in estimating total mortality in war zones, for example his estimate of 1.7 million deaths due to the war in the Congo which not only met with widespread acceptance and no challenge when published in 2000, but resulted and was cited in a U.N. Security Council resolution that all foreign armies must leave Congo, a United Nations request for $140 million in aid, and the US State Department pledging an additional $10 million in aid. Similar studies have been accepted uncritically as estimates of wartime mortality in Darfur and Bosnia.
Roberts' regular technique is to estimate mortality by personal surveys of a sample of the households in the area under study; this method being chosen in order to avoid the under-counting inherent in using only reported deaths in areas so chaotic that many deaths are unreported, and to include those deaths not directly attributable to violence but nevertheless the result of the conflict through indirect means, such as contamination of water supply or unavailability of medical care. The baseline mortality rate calculated from the interviewees' reports for the period prior to the conflict is subtracted from that reported during the conflict, to estimate the excess mortality which may be attributed to the presence of the conflict, directly or indirectly. This technique has been accepted uncritically in the previous mortality surveys discussed above.
Because of the impracticality of carrying out an evenly distributed survey, particularly during a war, Roberts' surveys use "cluster sampling", dividing the area into a number of randomly selected, approximately equally populated regions; a random point is chosen within each region, and a fixed number of the households closest to that point are surveyed as a "cluster". While not as accurate as an evenly distributed survey of the same number of households, this technique is more accurate than merely surveying one household for each selected point.
In his study of Iraq, Roberts divided the country into 36 regions, attempting to sample 30 households for each cluster, and selecting 988 households, with 7868 residents. In September 2004, each surveyed household was interviewed about household composition, births, and deaths since January 2002. Of 78 households where members were asked to show documentation to confirm their claims after the interview was finished, 63 were able to present death certificates. According to the authors, 5 (0.5%) of the 988 households that were randomly chosen to be surveyed refused to be interviewed.
The relative risk of death due to the 2003 invasion and occupation was estimated by comparing mortality in the 17.8 months after the invasion with the 14.6 months preceding it. The authors stated, "Making conservative assumptions, we think that about 100,000 excess deaths, or more have happened since the 2003 invasion of Iraq." Among such "conservative assumptions" is the exclusion of data from Fallujah in many of its findings. Since interpreting the results of the study would be complicated by the inclusion of an outlier cluster in Fallujah, where heavy fighting caused far more casualties than elsewhere in Iraq, the study focused mainly on the results that excluded the Fallujah cluster. While the authors argued that the Fallujah cluster's inclusion could be justified as a normal part of the sampling strategy (the authors noted that other "hotspots" like Najaf had not ended up being surveyed), and the authors presented two sets of results in some cases (one set including the Fallujah data and one not), the article, and most press coverage of the article, stresses the data that excluded the Fallujah cluster.
The main debate in the media in the U.S. and UK focused on whether 98,000 (95% CI 8000–194,000) more Iraqis died as a result of coalition intervention, calculated from their estimate of an increased mortality of 1.5 times (95% CI 1.1–2.3) the prewar rate (excluding the Fallujah data). Had the Fallujah sample been included, the survey's estimate that mortality rates had increased about 2.5 times since the invasion (with a 95% CI 1.6–4.2) including the Fallujah data would have resulted in an excess of about 298,000 deaths (95% CI ?–?), with 200,000 concentrated in the 3% of Iraq around Fallujah (Roberts et al. p. 5).
According to the article, violence was responsible for most of the extra deaths whether or not the Fallujah data was excluded. Coalition airstrikes would be the main cause of these violent deaths if Fallujah data were included. The study concluded that: "Violent deaths were widespread, reported in 15 of 33 clusters, and were mainly attributed to coalition forces." and "Violence accounted for most of the excess deaths and air strikes from coalition forces accounted for most violent deaths." The study estimates that the risk of death specifically from violence in Iraq during the period after the invasion was approximately 58 times higher than in the period before the war, with the CI95 being 8.1–419, meaning that there is a 97.5% chance that the risk of death from violence after the invasion is at least 8.1 times higher than it was before. Newsday reported:
The most common causes of death before the invasion of Iraq were heart attacks, strokes and other chronic diseases. However, after the invasion, violence was recorded as the primary cause of death and was mainly attributed to coalition forces—with about 95 percent of those deaths caused by bombs or fire from helicopter gunships.
Criticisms and countercriticisms Some criticisms have focused on the relatively broad 95% confidence intervals (CI95), resulting from the difficulty and scarcity of reliable sources."100,000 Deador 8,000. How many Iraqi civilians have died as a result of the war?". By Fred Kaplan. 29 October 2004. Slate.
Lila Guterman, after writing a long article in January 2005 in The Chronicle of Higher Education, wrote a short article in the Columbia Journalism Review that stated: "I called about ten biostatisticians and mortality experts. Not one of them took issue with the study's methods or its conclusions. If anything, the scientists told me, the authors had been cautious in their estimates. With a quick call to a statistician, reporters would have found that the probability forms a bell curve—the likelihood is very small that the number of deaths fell at either extreme of the range. It was very likely to fall near the middle.""Dead Iraqis. Why an Estimate was Ignored" . By Lila Guterman, Columbia Journalism Review, March/April 2005.
A Ministerial Statement written 17 November 2004, by the UK government stated "the Government does not accept its [the study's] central conclusion", because they were apparently inconsistent with figures published by the Iraq Ministry of Health, based on figures collected by hospitals, which said that "between 5 April 2004 and 5 October 2004, 3,853 civilians were killed and 15,517 were injured".
Some critics have said that The Lancet study authors were unable to visit certain randomly selected sample areas. In an interview on the radio program "This American Life" however, the authors of the study say that they never substituted different, more accessible, areas, and that every place that was randomly selected at the beginning of the study was surveyed in full, despite the risk of death to the surveyors.
Critics of the Lancet study have pointed out other difficulties in obtaining accurate statistics in a war zone. The authors of the study readily acknowledge this point and note the problems in the paper; for example they state that "there can be a dramatic clustering of deaths in wars where many die from bombings". They also said that the data their projections were based on were of "limited precision" because the quality of the information depended on the accuracy of the household interviews used for the study.