AFTER September 11th 2001, most countries beefed up security at airports and other vulnerable places. Tough-looking immigration officials no doubt made passengers feel safer, offsetting the irritation of longer queues. Yet doing something because it makes people feel good is not adequate justification. Is money devoted to counter-terrorism well spent?

What claims to be the first serious study of its costs and benefits, by economists at the Universities of Texas at Dallas and Alabama*, says no. It was commissioned by the Copenhagen Consensus, a think-tank that aims to scrutinise public spending on the world's woes and to ask “should we be starting from here?”




Terrorists react to incentives. If you tighten airport security, they hit trains. If you improve security at embassies, they kidnap businessmen. If you disrupt routine operations, they try deadlier ones. The authors reckon that, though the number of attacks and injuries has fallen since 2001, deaths have risen. Anti-terrorist spending displaces, as well as reduces, terrorism.

To get a sense of what might work better, the authors ask what would happen if spending were raised by 25%. Not much, they think: spending is inefficient now and would remain so. To see what might happen if there were more vigorous military action, they extrapolate from 2002-03, when America's belligerent response to September 11th was beginning. There were fewer terrorist attacks, they say, but the balance of costs and benefits is still poor—between five and eight cents of benefit for every dollar spent. But international co-operation to disrupt terrorist finances would be cost-effective, they think, producing $5-15 of benefits for each $1.

Given the uncertainties of the calculations, such figures can hardly be a blueprint for radically reordering spending priorities. But they are a reminder that throwing money at terrorism works no better than throwing money at anything else, and that some kinds of anti-terrorist spending are more efficient than others.

* “Transnational Terrorism”, by Todd Sandler, Daniel Arce and Walter Enders.