When the planes hit the twin towers eight years ago this week, I wasn't a journalist at all, but a business economist living in London. It was my job to look at what was happening to the economy and figure out what it might imply and what might happen next. Alongside the shock experienced by anyone watching the television coverage, I felt bewilderment. It seemed that the sheer physical destruction and the deaths of so many highly skilled people would have to disrupt the running of the US economy – one of Osama bin Laden's declared objectives. But with no close precedents, it was hard to say by how much.

Early estimates suggested that the economic cost alone might be grievous. The International Monetary Fund's World Economic Outlook, published three months after the attacks, thought that losses to the US economy could total $75bn. Others thought the economic damage would be greater. Robert E. Looney, a professor at the Naval Postgraduate School, estimated in 2002 that direct costs exceeded $27bn but the effect of the disruption might total $500bn. A study by the New York City Comptroller's Office estimated that the city alone would lose a cumulative $58bn between 2001 and 2004 as a result of the attacks.

Some attempts to untangle the question were ingenious. Alberto Abadie of Harvard and Sofia Dermisi of Roosevelt University looked not at New York but at Chicago to estimate one consequence of the attacks. Chicago, after all, suffered no damage and enjoyed no reconstruction boom. But as the home of the Sears Tower, the tallest building in the US, Chicago might have suffered a psychological blow as a possible target for a future attack. Sure enough, vacancy rates in and near the Sears Tower and two other famous Chicago skyscrapers rose sharply relative to rates elsewhere in the city.