But for those who are anxious about flying, statistical evidence will never be convincing. A similar phenomenon clouds the debate over whether Missourians should have the right to carry concealed weapons.

For many, the very idea is repellent, unthinkable. And yet, the statistical record strongly suggests that allowing law-abiding citizens to carry concealed weapons helps deter violent crime. Missouri voters will decide whether to approve such a law on April 6.

The most exhaustive attempt to document the concealed-weapon deterrent effect was conducted by John Lott Jr., former chief economist of the U.S. Sentencing Commission and now a professor at the University of Chicago School of Law.

Lott began with a simple question: Are criminals rational? Are they motivated by self-preservation?

Item: In Canada and Great Britain, which have strong gun control laws, about half of the break-ins are "hot burglaries," meaning they occur when the homeowner is present.

In the U.S. -- where the rate of gun ownership is much higher -- the hot burglary rate is only 13 percent.

Convicted felons responding to surveys say they’re less concerned about confronting police than armed citizens. If criminals are rational, then deterrence is a meaningful response. Concealed-carry laws should have a downward effect on violent crime, because such laws thwart a criminal’s effort to target potential victims who seem weak.

Lott tested this notion using a database with statistics on crime trends from all of the nation’s 3,054 counties between 1977 and 1992. He used sophisticated statistical techniques to isolate the effect of concealed-carry laws from other factors that influence crime, such as arrest rates.

His study makes for dense reading, but the most persuasive findings was this one: In all the states that adopted "shall-issue" concealed-carry laws -- under which officials must issue permits to qualified citizens -- violent crime dropped immediately or shortly after the law became effective.

Yes, crime runs in cycles. But as Lott points out, the drop in each state "...not only begin right when the laws pass but also take the crime rates well below what they had been before...it is difficult to believe that, on the average, state legislatures could have timed the passage of these laws so accurately as to coincide with the peaks of crime waves..."

The degree of crime reduction also correlates with the number of permits issued. In other words, more concealed weapons, more deterrence, which is why the title of Lott’s study, published in book form, is More Guns, Less Crime.

Opponents of concealed carry say allowing people to carry weapons will increase the violence generated by "road rage." Yet Lott reports that in 31 states with shall issue laws, some of which have been on the books for more than a decade, there is only one reported incident of such a shooting and that was in a Texas case that was ruled self-defense. I called Lott last week; the Texas incident is still the only recorded case of a permitted handgun being used in a traffic-related shooting.

Another hot-button issue is mass public shootings. Critics say the law would allow Missourians to carry handguns into day-care centers, onto school playgrounds and in other public places. It’s a politically effective argument because it implants a concrete and horrifying picture in people’s minds.

Yet in the concealed-carry states for which data were available, Lott found that the mean per capita death rate from such incidents fell by 69 percent.

The picture that ought to be in people’s minds is that of a citizen with a permitted handgun taking aim at a shooter about to commit mayhem in a public place. Lott recalls a 1984 incident in Jerusalem in which three terrorists brandished automatic weapons and fired, but were themselves shot by armed Israelis after only one victim had been killed. The surviving terrorist later told reporters his group had not realized Israeli citizens were armed.

More than 200 million guns exist in the United States. They're not likely to go away. At the very least, those who accept reality should look with an open mind toward any measure that increases the risk faced by violent criminals.