A few things you won’t hear about from the saturation coverage of the Newtown, Conn., school massacre:Mass shootings are no more common than they have been in past decades, despite the impression given by the media.In fact, the high point for mass killings in the U.S. was 1929, according to criminologist Grant Duwe of the Minnesota Department of Corrections.Incidents of mass murder in the U.S. declined from 42 in the 1990s to 26 in the first decade of this century.The chances of being killed in a mass shooting are about what they are for being struck by lightning.Until the...