Introduction

There has been widespread concern over the scale of Iraqi deaths after the invasion by the US-led coalition in March, 2003. Various methods have been used to count violent deaths, including hospital death data from the Ministry of Health, mortuary tallies, and media reports.1,2 The best known is the Iraq Body Count, which estimated that, up to September 26, 2006, between 43 491 and 48 283 Iraqis have been killed since the invasion.1 Estimates from the Iraqi Ministry of the Interior were 75% higher than those based on the Iraq Body Count from the same period.2 An Iraqi non-governmental organisation, Iraqiyun, estimated 128 000 deaths from the time of the invasion until July, 2005, by use of various sources, including household interviews.3

The US Department of Defence keeps some records of Iraqi deaths, despite initially denying that they did.4 Recently, Iraqi casualty data from the Multi-National Corps-Iraq (MNC-I) Significant Activities database were released.5 These data estimated the civilian casuality rate at 117 deaths per day between May, 2005, and June, 2006, on the basis of deaths that occurred in events to which the coalition responded. There also have been several surveys that assessed the burden of conflict on the population.6–8 These surveys have predictably produced substantially higher estimates than the passive surveillance reports.

Aside from violence, insufficient water supplies, non-functional sewerage, and restricted electricity supply also create health hazards.9,10 A deteriorating health service with insecure access, and the flight of health professionals adds further risks. People displaced by the on-going sectarian violence add to the number of vulnerable individuals. In many conflicts, these indirect causes have accounted for most civilian deaths.11,12

In 2004, we did a survey of 33 randomly selected clusters of 30 households with a mean of eight residents throughout Iraq to determine the excess mortality during the 17·8 months after the 2003 invasion.8 The survey estimated excess mortality of at least 98 000 (95% CI 8000–194 000) after excluding, as an outlier, the high mortality reported in the Falluja cluster. Over half of excess deaths recorded in the 2004 study were from violent causes, and about half of the violent deaths occurred in Falluja.

To determine how on-going events in Iraq have affected mortality rates subsequently, we repeated a national household survey between May and July, 2006. We measured deaths from January, 2002, to July, 2006, which included the period of the 2004 survey.

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Discussion

We estimate that, as a consequence of the coalition invasion of March 18, 2003, about 655 000 Iraqis have died above the number that would be expected in a non-conflict situation, which is equivalent to about 2·5% of the population in the study area. About 601 000 of these excess deaths were due to violent causes. Our estimate of the post-invasion crude mortality rate represents a doubling of the baseline mortality rate, which, by the Sphere standards, constitutes a humanitarian emergency.17

Our estimate of the pre-invasion crude or all-cause mortality rate is in close agreement with other sources.18,19 The post-invasion crude mortality rate increased significantly from pre-invasion figures, and showed a rising trend. The increasing number of violent deaths follows trends of bodies counted by mortuaries, as well as those reported in the media and by the Iraq Body Count.1,5,20

Application of the mortality rates reported here to the period of the 2004 survey8 gives an estimate of 112 000 (69 000–155 000) excess deaths in Iraq in that period. Thus, the data presented here validates our 2004 study, which conservatively estimated an excess mortality of nearly 100 000 as of September, 2004.

Our estimate of excess deaths is far higher than those reported in Iraq through passive surveillance measures.1,5 This discrepancy is not unexpected. Data from passive surveillance are rarely complete, even in stable circumstances, and are even less complete during conflict, when access is restricted and fatal events could be intentionally hidden. Aside from Bosnia,21 we can find no conflict situation where passive surveillance recorded more than 20% of the deaths measured by population-based methods. In several outbreaks, disease and death recorded by facility-based methods underestimated events by a factor of ten or more when compared with population-based estimates.11,22–25 Between 1960 and 1990, newspaper accounts of political deaths in Guatemala correctly reported over 50% of deaths in years of low violence but less than 5% in years of highest violence.26 Nevertheless, surveillance tallies are important in monitoring trends over time and in the provision of individual data, and these data track closely with our own findings (figure 4).

Mortality rates from violent causes have increased every year post-invasion. By mid-year 2006, 91 violent deaths had occurred in 6 months, compared with 27 post-invasion in 2003 and 77 in 2004, and 105 for 2005, suggesting that violence has escalated substantially. The attributed cause of these deaths has also changed with time. Our data show that gunfire is the major cause of death in Iraq, accounting for about half of all violent deaths. Deaths from air strikes were less commonly reported in 2006 than in 2003–04, but deaths from car explosions have increased since late 2005. The proportion of violent deaths attributed to coalition forces might have peaked in 2004; however, the actual number of Iraqi deaths attributed to coalition forces increased steadily through 2005. Deaths were not classified as being due to coalition forces if households had any uncertainty about the responsible party; consequently, the number of deaths and the proportion of violent deaths attributable to coalition forces could be conservative estimates. Distinguishing criminal murders from anti-coalition force actions was not possible in this survey.

Across Iraq, deaths and injuries from violent causes were concentrated in adolescent to middle age men. Although some were probably combatants, a number of factors would expose this group to more risk—eg, life style, automobile travel, and employment outside the home. The circumstances of a number of deaths from gunshots suggest assassinations or executions. Coalition forces have been reported as targeting all men of military age.27,28

From January, 2002, until the invasion in 2003, virtually all deaths in Iraq were from non-violent causes. The main causes of non-violent deaths were much the same as the leading causes of hospital deaths reported by the Ministry of Health in 2004 and 2005 (unpublished data). Death rates from non-violent causes remained essentially unchanged from pre-invasion levels until 2006, when they rose by 2·0 deaths per 1000 per year above the pre-invasion baseline, an increase that was not significant. We are unsure of the reason for the observed change in sex ratio of adults aged 15–59 years dying from non-violent causes between pre-invasion and post-invasion periods (table 2), or why deaths from cardiovascular causes rose after the invasion.

All surveys have potential for error and bias. The extreme insecurity during this survey could have introduced bias by restricting the size of teams, the number of supervisors, and the length of time that could be prudently spent in all locations, which in turn affected the size and nature of questionnaires. Further, calling back to households not available on the initial visit was felt to be too dangerous. Families, especially in households with combatants killed, could have hidden deaths. Under-reporting of infant deaths is a wide-spread concern in surveys of this type.29,30 Entire households could have been killed, leading to a survivor bias. The population data used for cluster selection were at least 2 years old, and if populations subsequently migrated from areas of high mortality to those with low mortality, the sample might have over-represented the high-mortality areas. The miscommunication that resulted in no clusters being interviewed in Duhuk and Muthanna resulted in our assuming that no excess deaths occurred in those provinces (with 5% of the population), which probably resulted in an underestimate of total deaths. Families could have reported deaths that did not occur, although this seems unlikely, since most reported deaths could be corroborated with a certificate. However, certificates might not be issued for young children, and in some places death certificates had stopped being issued; our 92% confirmation rate was therefore deemed to be reasonable.

Large-scale migration out of Iraq could affect our death estimates by decreasing population size. Out-migration could introduce inaccuracies if such a process took place predominantly in households with either high or low violent death history. Internal population movement would be less likely to affect results appreciably. However, the number of individual households with in-migration was much the same as those with out-migration in our survey.

Although interviewers used a robust process for identifying clusters, the potential exists for interviewers to be drawn to especially affected houses through conscious or unconscious processes. Although evidence of this bias does not exist, its potential cannot be dismissed.31 Furthermore, families might have misclassified information about the circumstances of death. Deaths could have been over or under-attributed to coalition forces on a consistent basis. The numbers of non-violent deaths were low, thus, estimation of trends with confidence was difficult. Not sampling two of the Governorates could have underestimated the total number of deaths, although these areas were generally known as low-violence Governorates. Finally, the sex of individuals who had died might not have been accurately reported by households. Female deaths could have been under-reported, or there might have been discomfort felt in reporting certain male deaths.

The striking similarity between the 2004 and 2006 estimates of pre-war mortality diminishes concerns about people's ability to recall deaths accurately over a 4-year period. Likewise, the similar patterns of mortality over time documented in our survey and by other sources corroborate our findings about the trends in mortality over time.1,5,32

In Iraq, as with other conflicts, civilians bear the consequences of warfare. In the Vietnam war, 3 million civilians died; in the Democratic Republic of the Congo, conflict has been responsible for 3·8 million deaths; and an estimated 200 000 of a total population of 800 000 died in conflict in East Timor.33–35 Recent estimates are that 200 000 people have died in Darfur over the past 31 months.36 We estimate that almost 655 000 people—2·5% of the population in the study area—have died in Iraq. Although such death rates might be common in times of war, the combination of a long duration and tens of millions of people affected has made this the deadliest international conflict of the 21st century, and should be of grave concern to everyone.

At the conclusion of our 2004 study8 we urged that an independent body assess the excess mortality that we saw in Iraq. This has not happened. We continue to believe that an independent international body to monitor compliance with the Geneva Conventions and other humanitarian standards in conflict is urgently needed. With reliable data, those voices that speak out for civilians trapped in conflict might be able to lessen the tragic human cost of future wars.

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