The Texas legislature is on the verge of passing a law permitting concealed weapons on University campuses, including the University of Texas where just this Fall my co-author Marcin Peski was holed up in his office waiting out a student who was roaming campus with an assault rifle.

This post won’t come to any conclusions, but I will try to lay out the arguments as I see them.  More guns, less crime requires two assumptions.  First, people will carry guns to protect themselves and second, gun-related crime will be reduced as a result.

There are two reasons that crime will be reduced: crime pays off less often, and sometimes it leads to shooting. In a perfect world, a gun-toting victim of a crime simply brandishes his gun and the criminal walks away or is apprehended and nobody gets hurt.  In that perfect world the decision to carry a gun is simple.  If there is any crime at all you should carry a gun becuase there are no costs and only benefits.  And then the decision of criminals is simple too:  crime doesn’t pay because everyone is carrying a gun.

(In equilibrium we will have a tiny bit of crime, just enough to make sure everyone still has an incentive to carry their guns.)

But the world is not perfect like that and when a gun-carrying criminal picks on a gun-carrying victim, there is a chance that either of them will be shot.  This changes the incentives.  Now your decision to carry a gun is a trade-off between the chance of being shot versus the cost of being the victim of a crime.  The people who will now choose to carry guns are those for whom the cost of being the victim of a crime outweigh the cost of an increased chance of getting shot.

If there are such people then there will be more guns.  These additional guns will reduce crime because criminals don’t want to be shot either.  In equilibrium there will be a marginal concealed-weapon carrier.  He’s the guy who, given the level of crime, is just indifferent between being a victim of crime and having a chance of being shot.  Everyone who is more willing to escape crime and/or more willing to face the risk of being shot will carry a gun.  Everyone else will not.

In this equilibrium there are more guns and less crime.  On the other hand there is no theoretical reason that this is a better outcome than no guns, more crime.  Because this market has externalities:  there will be more gun violence.  Indeed the key endogenous variable is the probability of a shootout if you carry a gun and/or commit a crime.  It must be high enough to deter crime.

And there may not be much effect on crime at all.  Whose elasticity with respect to increased probability of being shot is larger, the victim or the criminal?  Often the criminal has less to lose.  To deter crime the probability of a shooting may have to increase by more than victims are willing to accept and they may choose not to carry guns.

There is also a free-rider problem.  I would rather have you carry the gun than me.  So deterrence is underprovided.

Finally, you might say that things are different for crimes like mugging versus crimes like random shootings. But really the qualitative effects are the same and the only potential difference is in terms of magnitudes.  And it’s not obvious which way it goes.  Are random assailants more or less likely to be deterred?  As for the victims, on the one hand they have more to gain from carrying a gun when they are potentially faced with a campus shooter, but if they plan make use of their gun they also face a larger chance of getting shot.

NB:  nobody shot at the guy at UT in September and the only person he shot was himself.