I had a long talk the other day with a nice guy who disagrees with most of what I write about guns.

Scott Misus, of Worcester, Montgomery County, wanted to make sure I understood that Pennsylvania law allows gun owners to carry their weapons pretty much anywhere they want. He cherishes the freedom to protect himself and his children after living without it years ago in New Jersey.

"I carry when I go into cities for work or out to dinner with my family," Misus told me, "anyplace where I'm concerned for my safety."

I thought of my phone friend a few days later when University of Pennsylvania researchers released the results of a study seeking evidence that having a gun protects the holder from peril.

To the contrary, the epidemiologists found in the first-of-its-kind investigation: People with a gun on them were actually 4.5 times more likely to be shot than those who were unarmed.

"We're not saying gun possession causes you to be shot," warned lead researcher Charles Branas. "We're saying there's a correlation, a link."

That's some link, I tell him, predicting that message boards will light up as gun owners fire back.

After all, isn't protection the main reason anyone carries a gun?

Cause and effect?

The study, published in the American Journal of Public Health, focused on Philadelphia, where five people are shot each day. Comparing crime victims to a control group presents a host of "limitations," Branas said, but for now scientists have few other options.

"We can't randomly assign one group of people to have guns and another not to have them, then see what the outcome is," he said. "Even if we could do that, we'd have to wait a pretty long time for enough injury outcomes."

The language seems a mite dispassionate, but I'm intrigued by Branas' data. Both the shooting victims and the control group had a similar rate (6 percent) of gun possession, but 80 percent of the people shot were not in their house at the time. Meaning, they had a gun, they took it with them, and in a violent confrontation they fared no better than someone unarmed.

Branas conceded that more data - such as who fired first or whether victims pulled their weapons - could alter the scientific outcomes. So could knowing whether the shooting victims acquired their guns illegally.

"This is the beginning of the conversation," he explained. "This is how science progresses."

Protection isn't perfect

Carry laws differ greatly between Pennsylvania and New Jersey, mirroring the states' wildly opposing views on gun sales and ownership.

In New Jersey, where I live, 25,753 handguns were purchased last year, but only 580 people received carry permits.

"And the vast majority of those," notes State Police Det. Glenn Ross, "are for employment reasons," such as private detectives, armored car drivers, and security guards.

In Pennsylvania, 208,436 handguns were sold in 2008. And the bulk of those buyers - 150,840 - received licenses to carry.

Misus is one of them, but he favors concealing his weapon and never carries it poised to fire.

"A lot of these guys who carry open, I think they're nuts," he said. "I don't want the additional risk of having a round in the chamber at the Chinese buffet. I'm not comfortable with that."

When I told Misus about the Penn study, he wasn't the least bit convinced that it proves carrying a weapon is a pointless exercise.

"A guy got shot even though he had a gun?" Misus mocks. "Of course that happens."

We're talking about a criminal element, after all. Bad guys with illegal guns cause the crisis, but he and I disagree on the cure.

"My hypothesis is that the more people start carrying weapons and using them against crime, the fewer people are going to be committing crimes," he said. "Whether it's true or not, we still haven't seen."

Contact Monica Yant Kinney at myant@phillynews.com or 215-854-4670. Read her recent work at http://go.philly.com/yantkinney.