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Throughout conflicts, apologists for the side in power often excuse atrocities committed by their side with the claim that "violations are being committed on all sides of the conflict." The objective of such a statement is to render the parties morally equivalent, thereby relieving observers of the responsibility or duty to make a judgment about whether one side is the aggressor and the other is acting in self-defense. Even when the greater historical narrative involves more than these labels imply, in situations of massive human rights violations the perpetrators are rarely balanced in power. Although it may be literally true that all parties to a conflict have committed at least one violation, often the number of violations each party commits differs by a factor of ten or more relative to their opponents. In some cases quantitative analysis may offer a method for assessing claims about moral responsibility for crimes against humanity, including genocide. Statistics provide a way to measure crimes of policy—massive crimes that result from institutional or political decisions.

Although all parties may be guilty, they are rarely guilty in equal measure. Only with quantitative arguments can the true proportions of responsibility be understood. In this way one can transcend facile claims about "violations on all sides" in favor of an empirically rich view of responsibility for atrocities. Did the monthly number of killings increase or decrease in the first quarter of 1999? Were there more violations in Province A or in Province B? Were men more affected than women, or adults relative to children? These simple quantitative evaluations may be important questions when linked to political processes. Perhaps a new government took power and one needs to assess its impact on the state's respect for human rights. Or a military officer may move from Province A to Province B, and one may wish to determine if he is repeating the crimes he committed in Province A. Simple descriptive statistics based on properly gathered data can address these questions more precisely than the kinds of casual assessments that nonquantitative observers often make.

There are three areas in which nonquantitative analysts most often make statistical mistakes: estimating the total magnitude of violations; understanding how bias may have affected the data collection or interpretation; and comparing the relative proportions of responsibility among perpetrators. Poor information management and inappropriate statistical analysis can lead to embarrassing reversals of findings once proper methods are applied.

The use of statistical methods that demonstrably control biases and enable estimates of total magnitude can give analysts a rigorous basis for drawing conclusions about politically important questions. One such method, multiple systems estimation, uses three or more overlapping lists of some event (such as killings) to make a statistical estimate of the total number of events, including those events excluded from all three lists. "Overlapping" in this sense means events that are documented on two or more lists. The estimate made by this technique can control for several biases that might affect the original reporting which led to the lists of events.

For example, among the most important questions the Guatemalan Commission for Historical Clarification (CEH is the Spanish acronym) had to answer was whether the army had committed acts of genocide against the Maya. Using qualitative sources and field investigation, the CEH identified six regions in which genocide might have occurred. Data were collated from testimonies given to three sources: nongovernmental organizations (NGOs), the Catholic Church, and the CEH.

If genocide has been committed, then at least two statistical indicators should be clear. First, the absolute magnitude of the violations should be large. Second, there should be a big difference in the rate of killing between those who are in the victim group versus those people in the same region who are not in the victim group. It is inadequate to argue that some large number of people of specific ethnicities have been killed, because it might have been that they were simply unfortunate enough to live in very violent areas. Killing in an indiscriminate pattern might be evidence of some other crime, but if genocide occurred, a substantial difference in killing rates between targeted and nontargeted groups should exist. Thus, to find statistical evidence consistent with genocide, it is not enough that certain people were killed at high rate, but also that other nearby people were killed at much lower rates.

The CEH analysts conducted a multiple systems estimate of the total deaths of indigenous people and nonindigenous people between 1981 and 1983 in the six regions identified. For each group in each region, the estimated total number of deaths was divided into the Guatemalan government's census figures for indigenous and nonindigenous people in 1981. The CEH showed that resulting proportions were consistent with the genocide hypothesis. In each region indigenous people were killed at a rate five to eight times greater than nonindigenous people. This statistical finding was one of the bases of the CEH's final conclusion that the Guatemalan army committed acts of genocide against the Maya.

Other human rights projects have incorporated statistical reasoning. Sociologists and demographers have testified at the trial of Slobodan Milosevic and others tried before the International Criminal Tribunal for the Former Yugoslavia. They have provided quantitative insights on ethnic cleansing, forced migration, and the evaluation of explanatory hypotheses.

In the early twenty-first century, the statistical analysis of human rights violations is just beginning, and much work remains. New techniques should be developed, including easier methods for conducting random probability sampling in the field, richer demographic analysis of forced migration, and more flexible techniques for rapidly creating lots of graphical views of data. Human rights advocacy and analysis have benefited tremendously from the introduction of better statistical methods. The international community needs to continue to find new ways to employ existing methods, and to further research on new methods, so that human rights reporting becomes more rigorous. Statistics help establish the evidentiary basis of human rights allegations about crimes of policy.

SEE ALSO Forensics; Genocide; Massacres

Patrick Ball