Here are the Mass Public Shootings per Decade from the 1900s through 2012, adjusted for population. The rate is mass-shootings per million per decade, using the average population of the decade (or for the last data point, the average of the last three years 2010-2012).
The data are from Grant Duwe, director of research and evaluation at the Minnesota Department of Corrections, from his book Mass Murder in the United States: A History, reported by the Washington Post.
The paper presented the data in tabular form unadjusted for population. It looks better presented as a picture and accounting for the rise in census. The USA went from about 76 million in 1900 to around 315 million in 2012, so if the number of mass shootings remained “constant” we’d expect on average about about 4 times as many incidents this decade as there were in the 1900s just because of the increase in population.
According to the Post:
Duwe defines a mass public shooting as an incident in which four or more victims are killed publicly with guns within 24 hours — in the workplace, schools, restaurants and other public places — excluding shootings in connection with crimes such as robbery, drugs or gangs. (Note that this would exclude a number of “mass murders” that sometimes get lumped into the data, such as the Beltway sniper who killed 10 people over a three-week period in 2002.)
Note that these aren’t the number of murdered, but the number of separate incidents.
The Post took an interest in these data after Bill Clinton, perhaps missing the spotlight, on 9 January said, “Half of all mass killings in the United States have occurred since the assault weapons ban expired in 2005, half of all of them in the history of the country.”
Glenn Kessler who penned the article said, “the available data show that Clinton was way off base in his assertion, making an exaggerated claim — which his office would not even defend.” Kessler awarded “Three Pinocchios” for Clinton’s mendacity, and would have gone for the full four except for the “fuzziness of the data and questions about definitions”.
There is uncertainty. Why the bump in the 1930s and 1940s? It’s easy to explain by reference to that first great progressive experiment in Utopia, Prohibition, but Duwe excludes crimes due to “robbery, drugs or gangs”. Still, there may have been some spillover (of blood) from that first wave of what we can call, in honor of Hizzoner, Bloombergism and that era’s banning of booze.
There was also the Depression. The theory small paychecks are associated with mass shootings is bolstered by the increase in the 1970s and 80s, but the theory is then fractured because the number of incidents are now (apparently) falling, even though we are in one of the worst economic climates since the 1930s.
On the other hand, we only have three years of observation for this decade, so the uncertainty in what the remaining seven will bring is still high. On the last hand, the Depression was far worse than the recession and oil crises of the 70s and 80s, and the 1990s weren’t that bad at all, a time when the number of incidents peaked.
There were no violent video games in the Depression, but there was radio, replete with lurid programs, mostly about gang crime. The shows were thought to be a pernicious influence. Plenty of appalling, sick, twisted games now, however, but in the presence of dropping rates.
When it comes to the rate of gun ownership, that is higher in rural areas than in urban areas, but the murder rate is higher in urban areas. The rate of gun ownership is higher among whites than among blacks, but the murder rate is higher among blacks. For the country as a whole, handgun ownership doubled in the late 20th century, while the murder rate went down.
Gun ownership was also dropping through the 70s, 80s, and 90s, even though the mass-shooting rate increased.
In reality, like all complex social phenomena, the causes of these mass shootings are many, of unequal force, and changeable. Trying to pin the blame on any one culprit is a task best left to the dedicated.