Ann Coulter

In the wake of a monstrous crime like a madman's mass murder of defenseless women and children at the Newtown, Conn., elementary school, the nation's attention is riveted on what could have been done to prevent such a massacre.

Luckily, some years ago, two famed economists, William Landes at the University of Chicago and John Lott at Yale, conducted a massive study of multiple victim public shootings in the United States between 1977 and 1995 to see how various legal changes affected their frequency and death toll.

Landes and Lott examined many of the very policies being proposed right now in response to the Connecticut massacre: waiting periods and background checks for guns, the death penalty and increased penalties for committing a crime with a gun.

None of these policies had any effect on the frequency of, or carnage from, multiple-victim shootings. (I note that they did not look at reforming our lax mental health laws, presumably because the ACLU is working to keep dangerous nuts on the street in all 50 states.)

Only one public policy has ever been shown to reduce the death rate from such crimes: concealed-carry laws.

Their study controlled for age, sex, race, unemployment, retirement, poverty rates, state population, murder arrest rates, violent crime rates, and on and on.

The effect of concealed-carry laws in deterring mass public shootings was even greater than the impact of such laws on the murder rate generally.

Someone planning to commit a single murder in a concealed-carry state only has to weigh the odds of one person being armed. But a criminal planning to commit murder in a public place has to worry that anyone in the entire area might have a gun.

You will notice that most multiple-victim shootings occur in "gun-free zones" -- even within states that have concealed-carry laws: public schools, churches, Sikh temples, post offices, the movie theater where James Holmes committed mass murder, and the Portland, Ore., mall where a nut starting gunning down shoppers a few weeks ago.

Guns were banned in all these places. Mass killers may be crazy, but they're not stupid.

If the deterrent effect of concealed-carry laws seems surprising to you, that's because the media hide stories of armed citizens stopping mass shooters. At the Portland shooting, for example, no explanation was given for the amazing fact that the assailant managed to kill only two people in the mall during the busy Christmas season.