Imagine you're trying to protect your house from a break-in.
You put bars on all the windows, install dead-bolt locks, buy an alarm system and bump up your insurance.
Still feeling vulnerable, you wall off your property, build security gates, string razor wire, put surveillance cameras around the perimeter and hire 24-hour guards.
At some point, the tens of thousands of dollars worth of extra security exceeds any losses you might reasonably suffer in a robbery. And the chance of a theft is never completely eliminated.
That kind of calculation is a simple cost-benefit analysis. And there's always a tipping point, where additional spending starts to produce negligible benefits.
The death of Osama bin Laden, which coincides with a resumption of perimeter security talks between Canada and the United States, is a perfect opportunity to reflect on the costs and benefits of a decade of work to thwart another 9/11.
Provocative new research by Ohio State University national security professor John Mueller and engineering professor Mark Stewart of Australia's University of Newcastle suggests we may already have gone way too far. All the money spent by the U.S. to deter terrorism far exceeds any reasonable estimate of the toll of likely future attacks.
No one, for example, has bothered to do a full cost-benefit analysis of air marshals, border guards, body scanners, fences, drones, remote sensors and all the other post-9/11 realities. We do it for bridges, tax changes, major defence purchases, so why not security?
"Terrorism can inspire self-destructive overreaction like no other hazard, and this can be massively costly," Prof. Mueller and Prof. Stewart conclude in a new study, Terror, Security, and Money: Balancing the Risks, Benefits, and Costs of Homeland Security.
The study puts the cumulative increase in U.S. homeland security spending in the decade since 9/11 at more than $1-trillion (U.S.) - excluding the $150-billion-a-year cost of the wars in Iraq and Afghanistan. To justify this jaw-dropping sum, the extra security would have to deter an improbable 1,667 attacks every year on a scale of the foiled New York City Times Square bombing, according to their study.
That's because the frequency and severity of terrorist attacks remains relatively low. It's virtually impossible to justify a trillion dollars, based on "any rational and accepted standard of cost-benefit analysis," Prof. Mueller and Prof. Stewart argue.
"Like crime and vandalism, terrorism will always be a feature of life, and a condition of zero vulnerability is impossible to achieve," according to the study, which is the basis of a forthcoming book.
Justifying the money spent is "challenging, to say the least," the authors argue. And a lot of what's been spent is little more than "security theatre," doing little to reduce the threat of terrorism.
Prof. Mueller and Prof. Stewart get to a trillion dollars over 10 years by tallying the nearly $700-billion worth of increased spending on homeland security and intelligence by all levels of government and businesses. The remainder is made up of lost opportunity costs caused by increased insurance premiums, airport delays, road fatalities and the like.
These vast sums aren't just out of whack with the scale of the threat, they also create new problems. The study grimly points out that Muslim extremists have killed an estimated 200 to 300 people a year worldwide outside of war zones since 9/11. At the same time, delays and extra costs of enhanced airport security have prompted millions of people to drive rather than fly short-haul, resulting in clogged highways and more than 500 extra road deaths a year in the U.S. alone.
No similar calculations are available for Canada. The country has spent roughly $10-billion (Canadian) since 9/11 beefing up border security and emergency preparedness.
The conclusion too often reached by policy makers in both countries is that no amount of money spent on homeland security is too much.
Ottawa and Washington are now busily working out what their Declaration on a Shared Vision for Perimeter Security and Economic Competitiveness, signed in February, might ultimately mean. On the table for discussion are items such as better information sharing, co-ordinated entry-and-exit controls, customs preclearance and harmonized standards.
Canada's major business groups are hopeful that the talks will help unclog the now much-thicker border, saving them millions.
And in theory, moving toward a more secure Canada-U.S. perimeter should reduce costs and eliminate overlap.
But there's also a danger that too much effort is put into "security" and not enough on "competitiveness."
So before Canada commits to spending any more money on security, it's worth asking: For what?