Here’s a self-defense quiz.

Say you’re sitting at a bus stop in the District, alone at night, when a suspicious person approaches. There have been more than 475 robberies in the city this year — a 70 percent increase over this time last year — and many involve the theft of electronic devices such as smartphones.

But your chances of being victimized are greatly reduced because:

a. Your smartphone has a disabling device that makes it worthless to robbers.

b. More police officers have been assigned to street patrol.

c. You have a gun.

Police Chief Cathy Lanier believes the correct answers are (a) and (b). At a news conference last week, she said that a greater police presence has resulted in more than 100 arrests in robbery cases. In addition, police chiefs throughout the country will be lobbying the Federal Communications Commission, cellphone service providers and phone manufacturers to allow for the shutdown of stolen phones so that robbers can’t resell them on the black market.

“What’s going to stop this is stopping the profit,” Lanier said.

Of course, if you’re at that bus stop, you’d be more concerned about stopping a robber who will probably want more than just your cellphone. Some robbery victims have been beaten, sexually assaulted, stabbed and shot. Which brings us to a new report by the Cato Institute, a libertarian think tank based in Washington. It’s called: “Tough Targets: When Criminals Face Armed Resistance From Citizens.” As the title suggests, the authors would probably choose (c) as the best answer to the self-defense question.

“If policymakers are truly interested in harm reduction, they should pause to consider how many crimes — murders, rapes, assaults, robberies — are thwarted each year by ordinary persons with guns,” write Clayton E. Cramer, who teaches history at the College of Western Idaho, and David Burnett, director of public relations for Students for Concealed Carry.

Their report is based on roughly 5,000 news media accounts of self-defense with guns from October 2003 to November 2011. In making the case for carrying a concealed firearm, which is illegal in the District, the authors cite 285 news stories about defenders who had licenses to carry a gun, most of whom had used their weapons to successfully thwart street robberies.

In one story, on May 5, 2010, a St. Louis man was robbed at gunpoint. While the robber was going through his wallet, the man pulled his own gun and killed the assailant.

“Many people support gun control regulations because they are convinced that the average citizen is either incapable of using a gun in self-defense or will use the gun in a fit of anger over some petty matter,” the authors write. “Those assumptions are false.”

Nevertheless, even the most fervent gun advocates doubt that simply carrying a gun on the streets will guarantee your safety. George Lyon, a District resident and plaintiff in a lawsuit to legalize carrying a concealed firearm in the city, explained to me what could happen if someone wearing a gun in a holster was approached by robber wielding a knife.

“A person armed with a contact weapon like a club or a knife can travel about seven yards in two seconds,” Lyon said. “And 1.5 seconds is about the minimum time it takes for a trained person to react, present a firearm and get off one or two shots. So, in all likelihood, unless you are very aware of your situation and looking for attack cues, you are going to get stabbed by the assailant. Having said that, I still believe a gun is a much better self-defense or emergency-rescue tool than a knife.”

Back to the bus stop example, which comes from a D.C. police crime report on Feb. 14: A woman was sitting at a bus stop on 11th Street NW about 1:30 a.m. when she was robbed of a laptop, cellphone, books, cash and credit cards.

Was the woman at fault for being out that late, carrying so many valuable items? Can she really expect to sit at a bus stop at any hour and not be targeted by criminals?

Risk avoidance — add that to the multiple-choice self-defense quiz.