Correction: The violent death toll from the Iraq War: 2003-2023.

[This corrects the article DOI: 10.1371/journal.pone.0297895.].

The violent death toll from the Iraq War: 2003-2023.

From the beginning of the Iraq war, in March of 2003, to the present day, controversy has swirled around the death toll of the war. This paper narrows down the range of uncertainty for the numbers and trends in violent deaths in the war. I assemble and appraise all primary sources that cover the period from March of 2003 onwards-six sample surveys plus a casualty recording project (Iraq Body Count [IBC]). Data permitting, I present cumulative monthly figures with, for the surveys, 95% bootstrapped uncertainty intervals. The analysis uncovers a core of high-quality mainstream sources that are highly consistent with each another. In addition, there are three outlier surveys that are compromised by serious flaws and produce estimates far outside the mainstream. Discarding the outlying and flawed surveys reveals a clear picture of the violent death toll from the Iraq war. IBC figures, extended to include combatants, occupy a central position within the mainstream range of estimates. The strong consistency across the high-quality sources provides a rare validation of three war-death-measurement methodologies-household-based surveys, sibling-based surveys, and casualty recording. Methodological success notwithstanding, we must transcend the numbers to truly comprehend the human costs of the war.

Unifying casualty distributions within and across conflicts.

The distribution of whole war sizes and the distribution of event sizes within individual wars, can both be well approximated by power laws where size is measured by the number of fatalities. However the power-law exponent value for whole wars has a substantially smaller magnitude - and hence a flatter distribution - than for individual wars. We provide detailed numerical evidence that confirms that these numerically different power-law exponent values are interrelated in a simple way by the effect of aggregating fatalities from individual events within wars to whole wars. We offer intuition for this finding and hence strengthen the case for a unified description and understanding of human conflict across scales.

Fundamental patterns and predictions of event size distributions in modern wars and terrorist campaigns.

It is still unknown whether there is some deep structure to modern wars and terrorist campaigns that could, for example, enable reliable prediction of future patterns of violent events. Recent war research focuses on size distributions of violent events, with size defined by the number of people killed in each event. Event size distributions within previously available datasets, for both armed conflicts and for global terrorism as a whole, exhibit extraordinary regularities that transcend specifics of time and place. These distributions have been well modelled by a narrow range of power laws that are, in turn, supported by some theories of violent group dynamics. We show that the predicted event-size patterns emerge broadly in a mass of new event data covering all conflicts in the world from 1989 to 2016. Moreover, there are similar regularities in the events generated by individual terrorist organizations, 1998-2016. The existence of such robust empirical patterns hints at the predictability of size distributions of violent events in future wars. We pursue this prospect using split-sample techniques that help us to make useful out-of-sample predictions. Power-law-based prediction systems outperform lognormal-based systems. We conclude that there is indeed evidence from the existing data that fundamental patterns do exist, and that these can allow prediction of size distribution of events in modern wars and terrorist campaigns.

Attacks on medical workers in Syria: Implications for conflict research.

In a Perspective linked to the Research Article by Haar and colleagues, Michael Spagat discusses the challenges and importance of conducting research on mortality in regions affected by violent conflicts.

Simple mathematical law benchmarks human confrontations.

Many high-profile societal problems involve an individual or group repeatedly attacking another - from child-parent disputes, sexual violence against women, civil unrest, violent conflicts and acts of terror, to current cyber-attacks on national infrastructure and ultrafast cyber-trades attacking stockholders. There is an urgent need to quantify the likely severity and timing of such future acts, shed light on likely perpetrators, and identify intervention strategies. Here we present a combined analysis of multiple datasets across all these domains which account for >100,000 events, and show that a simple mathematical law can benchmark them all. We derive this benchmark and interpret it, using a minimal mechanistic model grounded by state-of-the-art fieldwork. Our findings provide quantitative predictions concerning future attacks; a tool to help detect common perpetrators and abnormal behaviors; insight into the trajectory of a 'lone wolf'; identification of a critical threshold for spreading a message or idea among perpetrators; an intervention strategy to erode the most lethal clusters; and more broadly, a quantitative starting point for cross-disciplinary theorizing about human aggression at the individual and group level, in both real and online worlds.

Global comparison of warring groups in 2002-2007: fatalities from targeting civilians vs. fighting battles.

BACKGROUND: Warring groups that compete to dominate a civilian population confront contending behavioral options: target civilians or battle the enemy. We aimed to describe degrees to which combatant groups concentrated lethal behavior into intentionally targeting civilians as opposed to engaging in battle with opponents in contemporary armed conflict. METHODOLOGY/PRINCIPAL FINDINGS: We identified all 226 formally organized state and non-state groups (i.e. actors) that engaged in lethal armed conflict during 2002-2007: 43 state and 183 non-state. We summed civilians killed by an actor's intentional targeting with civilians and combatants killed in battles in which the actor was involved for total fatalities associated with each actor, indicating overall scale of armed conflict. We used a Civilian Targeting Index (CTI), defined as the proportion of total fatalities caused by intentional targeting of civilians, to measure the concentration of lethal behavior into civilian targeting. We report actor-specific findings and four significant trends: 1.) 61% of all 226 actors (95% CI 55% to 67%) refrained from targeting civilians. 2.) Logistic regression showed actors were more likely to have targeted civilians if conflict duration was three or more years rather than one year. 3.) In the 88 actors that targeted civilians, multiple regressions showed an inverse correlation between CTI values and the total number of fatalities. Conflict duration of three or more years was associated with lower CTI values than conflict duration of one year. 4.) When conflict scale and duration were accounted for, state and non-state actors did not differ. We describe civilian targeting by actors in prolonged conflict. We discuss comparable patterns found in nature and interdisciplinary research. CONCLUSIONS/SIGNIFICANCE: Most warring groups in 2002-2007 did not target civilians. Warring groups that targeted civilians in small-scale, brief conflict concentrated more lethal behavior into targeting civilians, and less into battles, than groups in larger-scale, longer conflict.

Casualties in civilians and coalition soldiers from suicide bombings in Iraq, 2003-10: a descriptive study.

BACKGROUND: Suicide bombs in Iraq are a major public health problem. We aimed to describe documented casualties from suicide bombs in Iraq during 2003-10 in Iraqi civilians and coalition soldiers. METHODS: In this descriptive study, we analysed and compared suicide bomb casualties in Iraq that were documented in two datasets covering March 20, 2003, to Dec 31, 2010--one reporting coalition-soldier deaths from suicide bombs, the other reporting deaths and injuries of Iraqi civilians from armed violence. We analysed deaths and injuries over time, by bomb subtype and victim demographics. FINDINGS: In 2003-10, 1003 documented suicide bomb events caused 19% (42,928 of 225,789) of all Iraqi civilian casualties in our dataset, 26% (30,644 of 117,165) of injured civilians, and 11% (12,284 of 108,624) of civilian deaths. The injured-to-killed ratio for civilians was 2·5 people injured to one person killed from suicide bombs. Suicide bombers on foot caused 43% (5314 of 12,284) of documented suicide bomb deaths. Suicide bombers who used cars caused 40% (12,224 of 30,644) of civilian injuries. Of 3963 demographically identifiable suicide bomb fatalities, 2981 (75%) were men, 428 (11%) were women, and 554 (14%) were children. Children made up a higher proportion of demographically identifiable deaths from suicide bombings than from general armed violence (9%, 3669 of 40,276 deaths; p<0·0001). The injured-to-killed ratio for all suicide bombings was slightly higher for women than it was for men (p=0·02), but the ratio for children was lower than it was for both women (p<0·0001) and men (p=0·0002). 200 coalition soldiers were killed in 79 suicide bomb events during 2003-10. More Iraqi civilians per lethal event were killed than were coalition soldiers (12 vs 3; p=0·004). INTERPRETATION: Suicide bombers in Iraq kill significantly more Iraqi civilians than coalition soldiers. Among civilians, children are more likely to die than adults when injured by suicide bombs. FUNDING: None.

Violent deaths of Iraqi civilians, 2003-2008: analysis by perpetrator, weapon, time, and location.

BACKGROUND: Armed violence is a major public health and humanitarian problem in Iraq. In this descriptive statistical analysis we aimed to describe for the first time Iraqi civilian deaths caused by perpetrators of armed violence during the first 5 years of the Iraq war: over time; by weapon used; by region (governorate); and by victim demographics. METHODS AND FINDINGS: We analyzed the Iraq Body Count database of 92,614 Iraqi civilian direct deaths from armed violence occurring from March 20, 2003 through March 19, 2008, of which Unknown perpetrators caused 74% of deaths (n = 68,396), Coalition forces 12% (n = 11,516), and Anti-Coalition forces 11% (n = 9,954). We analyzed the subset of 60,481 civilian deaths from 14,196 short-duration events of lethal violence to link individual civilian deaths to events involving perpetrators and their methods. One-third of civilian violent death was from extrajudicial executions by Unknown perpetrators; quadratic regression shows these deaths progressively and disproportionately increased as deaths from other forms of violence increased across Iraq's governorates. The highest average number of civilians killed per event in which a civilian died were in Unknown perpetrator suicide bombings targeting civilians (19 per lethal event) and Coalition aerial bombings (17 per lethal event). In temporal analysis, numbers of civilian deaths from Coalition air attacks, and woman and child deaths from Coalition forces, peaked during the invasion. We applied a Woman and Child "Dirty War Index" (DWI), measuring the proportion of women and children among civilian deaths of known demographic status, to the 22,066 civilian victims identified as men, women, or children to indicate relatively indiscriminate perpetrator effects. DWI findings suggest the most indiscriminate effects on women and children were from Unknown perpetrators using mortar fire (DWI  = 79) and nonsuicide vehicle bombs (DWI  = 54) and from Coalition air attacks (DWI  = 69). Coalition forces had higher Woman and Child DWIs than Anti-Coalition forces, with no evidence of decrease over 2003-2008, for all weapons combined and for small arms gunfire, specifically. CONCLUSIONS: Most Iraqi civilian violent deaths during 2003-2008 of the Iraq war were inflicted by Unknown perpetrators, primarily through extrajudicial executions that disproportionately increased in regions with greater numbers of violent deaths. Unknown perpetrators using suicide bombs, vehicle bombs, and mortars had highly lethal and indiscriminate effects on the Iraqi civilians they targeted. Deaths caused by Coalition forces of Iraqi civilians, women, and children peaked during the invasion period, with relatively indiscriminate effects from aerial weapons. Please see later in the article for the Editors' Summary.

Common ecology quantifies human insurgency.

Many collective human activities, including violence, have been shown to exhibit universal patterns. The size distributions of casualties both in whole wars from 1816 to 1980 and terrorist attacks have separately been shown to follow approximate power-law distributions. However, the possibility of universal patterns ranging across wars in the size distribution or timing of within-conflict events has barely been explored. Here we show that the sizes and timing of violent events within different insurgent conflicts exhibit remarkable similarities. We propose a unified model of human insurgency that reproduces these commonalities, and explains conflict-specific variations quantitatively in terms of underlying rules of engagement. Our model treats each insurgent population as an ecology of dynamically evolving, self-organized groups following common decision-making processes. Our model is consistent with several recent hypotheses about modern insurgency, is robust to many generalizations, and establishes a quantitative connection between human insurgency, global terrorism and ecology. Its similarity to financial market models provides a surprising link between violent and non-violent forms of human behaviour.