Guatemala 1993-1999 – Using MSE to Estimate the Number of Deaths

Propelled by the impact of data analysis in El Salvador, Patrick Ball applied his WDWTW model to human rights information in other countries. Throughout the 1990’s, Ball worked at the American Association for the Advancement of Science (AAAS) analyzing large-scale human rights violations in Ethiopia, South Africa, Haiti and Guatemala. Together with senior scientific colleagues, including statistician Dr. Herb Spirer, Ball developed new methods for analyzing state-sanctioned violence. This chapter documents how the research expanded when a group of nongovernmental organizations in Guatemala asked the scientific community to gather and analyze information about human rights violations in that country. Ball advised the International Center for Human Rights Research in Guatemala (CIIDH) as they collected evidence from testimonies and press reports of more than 43,000 human rights violations during the country’s 36-years of armed conflict. Ball assembled this data into a database protected by PGP encryption software.


After the 1996 UN-brokered peace accords in Guatemala, Ball’s database became a valuable source of information for the Commission for Historical Clarification (CEH) which asked the AAAS to determine how many people were killed in Guatemala from 1960 to 1996. Ball created a large information management system to analyze the reported human rights violations and patterns of violence. He developed methods to remove duplicate reports and control for statistical bias in observed human rights data. This allowed Ball to apply a statistical technique suggested by HRDAG statistician Fritz Scheuren called multiple systems estimation (MSE) that uses overlapping accounts to estimate the number of unreported events. Using MSE, Ball and his colleagues estimated the number of unreported victims by comparing three databases of human rights information. HRDAG analysts determined that there were approximately 132,174 killings that took place in Guatemala between 1978 and 1996 with a standard error of 6,568. These included approximately 84,468 killings that were never reported. The CEH also found that acts of genocide were committed against indigenous Mayan communities.

Our work has been used by truth commissions, international criminal tribunals, and non-governmental human rights organizations. We have worked with partners on projects on five continents.