How many homicides were there in 2010 in the United States? Well, that’s easy. Let’s just do some Googling:
Between the smallest and largest figures there is a difference of 3,292 deaths or 25%!
The differences are striking but not entirely arbitrary or without explanation. I assume the second figure adds late additions to the 2010 data and so should be considered more authoritative but that is a relatively small difference.
The difference between 2 and 3 is puzzling and seems to be that the number in 2 is drawn from the Supplementary Homicide Report (SHR) statistics on victims while the larger figure is drawn from homicide reports in the UCR. Not all agencies collect the more detailed statistics in the SHR while the UCR is nearly complete. Thus the victim figure is smaller than the report figure (this doesn’t appear to conform exactly to where the data is supposed to be sourced but it’s what the FBI tells me). It’s unclear why the FBI would report both figures when they know one is misleading.
The difference between 3 and 4 comes from different definitions of homicide. The FBI collects data on crimes. If a killing is ruled justified, i.e. not a crime, it doesn’t go into the FBI homicide statistics. The CDC collects data from death certificates which list as homicide any death caused by “injuries inflicted by another person with intent to injure or kill, by any means.” Thus, the CDC data includes justifiable homicide. In 2010 according to the FBI there were 387 justifiable homicides by law enforcement and 278 by private citizen for a total of 665 justifiable homicides, so that accounts for some but not all of the difference.
(By the way, the 278 justifiable homicides in 2010 by private citizens compared to 387 by law enforcement and 14,720 unjustifiable homicides would seem to be an important context for many claims about stand your ground laws. N.b. this doesn’t mean that the laws couldn’t be associated with more unjustifiable homicides).
The FBI (3) and NVSS (4) figures track each other closely over time but its important to be aware of the differences and to be consistent in one’s calculations.