ITH A GUNMAN'S attack that killed seven people at a Wakefield Internet company on Tuesday, the question is simple: What can be done to stop similar shootings in the future?

For many the answer is more government regulation. The creation of gun-free zones, waiting periods, background checks, and safe storage regulations are just a few of the laws typically proposed. Yet, Massachusetts already has these restrictions and many more.

Surely the intentions of these laws are noble. The goal of preventing concealed handguns or creating gun-free zones is to protect people. But what might appear to be the most obvious policy may actually cost lives.

When gun control laws are passed, it is law-abiding citizens, not would-be criminals, who obey them. Unfortunately, the police cannot be everywhere, so these laws risk creating situations in which the good guys cannot defend themselves from the bad ones.

This point was driven home to me when I received an e-mail from a friend recently, telling me that he had just dropped off his kids at a public school and outside the school was a sign that said ''This is a gun-free zone.'' I couldn't help think, if I put up a sign on my home that said, ''This home is a gun-free zone,'' would it make it more attractive or less attractive to criminals entering my home and attacking myself or my family?

While horrible crimes like the one in Wakefield get the attention they deserve, rarely mentioned are the many attacks that are stopped by citizens who are able to defend themselves. About two million times a year people use guns defensively. Few realize that some of the public school shootings were stopped by citizens with guns.

For example, in the first public shooting spree at a high school, in Pearl, Miss., in October 1997 that left two dead, an assistant principal retrieved a gun from his car and physically immobilized the shooter for more than five minutes before police arrived.

A school-related shooting in Edinboro, Pa., in spring 1998 that left one dead, was stopped after a bystander pointed a shotgun at the shooter when he started to reload his gun. The police did not arrive for another 11 minutes.

But anecdotal stories cannot resolve this debate. A study at the University of Chicago by a colleague and myself compiled data on all of the multiple-victim public shootings that occurred in the United States from 1977 to 1999. Included were incidents in which at least two people were killed or injured in a public place; to focus on the type of shooting seen in Wakefield, we excluded gang wars or shootings that were the byproduct of another crime, such as robbery. The United States averaged more than 20 such shootings annually, with an average of 1.5 people killed and 2.5 wounded in each one.

So what can stop these attacks? We have examined a range of different gun laws, such as waiting periods, as well the frequency and level of punishment. However, while arrest and conviction rates, prison sentences, and the death penalty reduce murders generally, they do not consistently deter public shootings.

The reason is simple: Those who commit these crimes usually die. They are either killed in the attack or commit suicide. The normal penalties rarely apply.

To be effective, policies must deal with what motivates these criminals, which is to kill and injure as many people as possible. Some appear to do it for the publicity, which is itself related to the amount of harm they inflict.

The best way to stop these attacks is to enact policies that can limit the carnage. We found only one policy that effectively accomplishes this: the passage of right-to-carry laws.

With Michigan's adoption this month, 32 states now give adults the right to carry concealed handguns as long as they do not have a criminal record or a history of significant mental illness. When states passed such laws during the 23 years we studied, the number of multiple-victim public shootings declined by a dramatic 67 percent. Deaths and injuries from these shootings fell on average by 78 percent.

To the extent that attacks still occur in states after these laws are enacted, they disproportionately occur in areas in which concealed handguns are forbidden. The people who get these permits are extremely law-abiding and rarely lose their permits for any reason. Without letting law-abiding citizens defend themselves, we risk leaving victims as sitting ducks.