The recent killings of several unarmed black men by police have prompted outrage throughout the country.  Amid calls for sanctions and police training reforms, governments, policymakers, and researchers alike are scrambling to figure out just how widespread the problem is.  This is a tricky endeavor because "no one collects data that answers exactly that question. There is no national database that police departments are required to submit a record to when they complete an investigation after a police officer shoots a civilian."

The interactive map below is based on data from Fatal Encounters, a nonprofit trying to build a national database of police killings from reports from the public, media, and FBI. It shows some of the deaths by law enforcement since 2000.  The creator of Fatal Encounters estimates that the database captures only 35 percent of police killings.


The only official (i.e. governmental) source of data on police killings is the FBI's Supplemental Homicide Reports (SHR).  The SHR, published annually, contain information about "justifiable homicides," which can be used as a very imperfect proxy for police killings (note: there's no effort at all to record the number of unjustifiable homicides by police).

The SHR statistics are problematic for a number of reasons, as explained in this article by FiveThirtyEight:

1. As is the case for the FBI's Uniform Crime Reports (UCR), the SHR rely on voluntary reports by police agencies.  But fewer local police agencies report SHR data than report standard Uniform Crime Reports data and some states, like Florida, don't participate at all.
2. "Felon killed by police" refers narrowly to justifiable police homicides, and "unjustifiable homicide by police" is not a classification. This means it's difficult to combine unjustifiable police homicides — which could be listed as crimes elsewhere in the database — with "justifiable" police homicides.
3. It's likely there are homicides recorded in the SHR that should be attributed to police as "justifiable" but aren't. And there's an unknown number of unjustifiable police homicides that aren't marked with any evidence of police involvement.
4. If the legality of a police homicide is in question, it may not be reported to the SHR until the investigation is resolved. If the investigation concludes in a new reporting year, the old SHR data may not be updated, regardless of whether the killing was found to be justifiable or not. Criminology professor Geoff Alpert of the University of South Carolina, an expert on police violence, said he has "never seen a department go back and audit their numbers and fix them." (In a statement provided in response to emailed questions, the FBI confirmed that it generally does not reopen master data files to add or correct reports.)
5. Killings in federal jurisdictions, such as federal prisons or military bases, are not included in the database.

As a result of these flaws, a study from the Bureau of Justice Statistics estimates that official statistics under-count the number of people killed by police by more than half.  According to criminologist David Klinger (University of Missouri, St. Louis): "The available data (FBI, Vital Stats, BJS) are worse than miserable.  They suck and no one should do any sort of analysis with them beyond using them to say that we have some floor [regarding] shootings and perhaps note that there are all sorts of circumstances involved when shootings occur."

The SHR do contain some information about the demographic characteristics of both victims and perpetrators of homicides, as well as the circumstances surrounding the homicide.  For example, there are six different subcategories of "felon killed by an officer": attacking the officer, attempting flight, killed in the commission of a crime, resisting arrest, ... However the reports often rely on the word of the officer involved in the killing and contain no information about whether victims were armed when killed by police.

It difficult, if not impossible, to know the actual level of racial disparities in police use of force, but an analysis of SHR "justifiable homicides" in 2012 suggests that victims of "justifiable homicide" are "overwhelmingly male, heavily young, disproportionately black," and that the majority were not attacking anyone when they were killed.

Note: The dark (or hidden) figure of crime is a term employed by criminologists and sociologists to describe the amount of unreported or undiscovered crime.

Read more:
http://www.vox.com/2014/12/17/7408455/police-shootings-map
http://www.fatalencounters.org/
http://www.vox.com/2014/8/21/6051043/how-many-people-killed-police-statistics-homicide-official-black
http://www.washingtonpost.com/sf/investigative/2015/04/11/thousands-dead-few-prosecuted/
http://fivethirtyeight.com/features/how-many-americans-the-police-kill-each-year/
http://www.bjs.gov/index.cfm?ty=pbdetail&iid=5259

TeachingwithData.org resources:
Gun Violence in America (http://www.teachingwithdata.org/resource/3864)
Fear of Crime (http://www.teachingwithdata.org/resource/3155)
Crime Victimization in the US: A Data-Driven Learning Guide (http://www.teachingwithdata.org/resource/3437)
Generational Trends in Attitudes about Gun Ownership: A Data-Driven Learning Guide (http://www.teachingwithdata.org/resource/3448)
Crime and Victims Statistics (http://www.teachingwithdata.org/resource/3261)