How reliable are Mexican Homicide Statistics?
There are 2 main sources of homicide statistics in Mexico, the vital statistics from the INEGI, and the police data which are available at the ICESI (a civic association not affiliate with the government which gets the data from the SNSP [Secretaría Nacional de Seguridad Pública]). But as it turns out the data from the ICESI is only an estimate (even if the secretary of the interior uses the data in his presentations as if it were the number of homicides), still, you can download the final numbers from the Statistical Yearbooks of each state. Since both data sources are available at the state level you can compare them and see if there are any differences.
The plot gets thicker: it turns out the data from the ICESI for 2008 are only estimates (missing over 1,100 homicides in Chihuahua, looks like it was a mid-year "estimate"). The INEGI releases a series of statistical yearkbooks for each state that contain the final (final being over 90% reported) data according to the local police forces (homicide is a local crime in Mexico). I didn't include the statistical yearbooks because they're about 250MB, but in the directory "stat-yearbooks" you'll find a script to download them
Even thicker: the data from the ICESI and the statistical yearbooks are not even homicides, but police reports. So if 18 kids are killed in a massacre at the same time, and there's only one police report, they are recorded as one. The statistical yearbooks do have the data available by number of victims, but they combine "homicidios dolosos" (homicide) with "homicidios culposos" (manslaughter). I wonder, wonder why they would do this?
Data are also available from PAHO and the UN, but only at the national level.
Since the INEGI database failed to follow Benford's law I also checked to see if some of the big massacres that occurred in Mexico were recorded, not surprisingly some of them were not in the database
- Chart of homicides rate according to the INEGI, ICESI, PAHO, and the UN Crime Survey.
- Bar plot of the differences in number if homicides, one for the ICESI data and another for the final data from the Statistical Yearbooks.
- Scatter plot of the different homicide data (INEGI vs ICESI). That is see if the police records (labeled ICESI) match those of the vital statistics system(labeled INEGI). The police records are missing over 1,100 homicides in Chihuahua alone.
- Scatter plot against the proportions.
- A csv file with the number of homicides in the months during which there were massacres
Mexican Homicide Data:
Statistical Yearbooks: The following states were not available as of Feb-17-2009, so I used the estimates that appear in the file from the ICESI: Durango, Tlaxcala, Yucatan and Nayarit. Furthermore, there was a mistake in the statistical yearbook for Querétaro (the values from "homicidios dolosos"[homicide] and "homicidios culposos"[manslaughter] was transposed).
PAHO Pan American Health Organization, Health Analysis and Statistics Unit. Regional Core Health Data Initiative; Technical Health Information System. Washington DC, 2007.
UN Crime Survey: Eight and Seventh United Nations Survey of Crime Trends and Operations of Criminal Justice Systems
Aguas Blancas Massacre: (Warning: Graphic Video) 17 dead, June 28, 1995. In the INEGI homicide database
Acteal Massacre: 45 dead ,December 22, 1997. Not in the INEGI homicide database
Decapitated Bodies in Yucatán: August 28 2008, 12 dead. In the INEGI homicide database
Arizpe-Cananea: May 16, 2007, 22 dead. In the INEGI homicide database
Tijuana prison riot: September 2008, 25 dead. In the INEGI homicide database
Reynosa prison riot: October 2008, 21 dead. In the INEGI homicide database
Ensenada: September 19, 1998, 18 dead. In the INEGI homidice database
24 dead outside Mexico City: September 13, 2008, 24 dead. In the INEGI homicide database
Colums: State | INEGI | ICESI | Abbrv | Anuario | Stat.Yrbks
State - Name of the State
INEGI - Number of homicides according to the INEGI
ICESI - Number of homicides according to the ICESI (which takes the data from SNSP)
Anuario - The raw values according to the Statistical Yearbooks
Stat.Yrbks - The values from the Statistical Yearbooks if available, if not, the data is from the ICESI