For the second time in two days, CNN went out of its way to debunk the Michael Bloomberg/Barack Obama claim that mass shootings have become epidemic and a “new normal” in American society. The day after CNN debunked the Bloomberg-funded Everytown claim that there were 74 Newtown-style mass shootings since Sandy Hook, Jake Tapper interviewed Northeastern University criminology professor James Alan Fox to look at the data rather than the anecdotes. Over a 40-year period, Fox concluded, mass shootings have remained flat — even while the population of the country has grown significantly over the same period:

So are mass shootings on the rise? One professor and criminologist says no. Northeastern University criminology professor James Alan Fox compiled the data of shootings with four or more fatalities from 1976 to 2012, and found that these incidents on a chart look like an EKG: up and down, not a steady rise.

Fox doesn’t mention the other trendline on overall gun violence, which isn’t flat — it’s falling, on both the actual numbers and especially on a population-adjusted basis. The trend began during the Clinton administration, but accelerated after the expiration of the so-called “assault weapon” ban. The 1994 ban did not cause the rate of mass shootings to fall, either, mainly because most of those involved handguns (and shotguns) rather than rifles.

Fox tells Tapper that people should take Bill Clinton’s advice from that period to look at trend lines rather than headlines. They should also take care to make sure the data for those trend lines is honestly compiled, rather than cobbled together for maximum hysteria and political impact.