Economists disagree on what constitutes a recession. The most common definition is a fall in real (inflation-adjusted) gross domestic product – the standard wealth measure for an economy – for two or more quarters in a row. Others argue that depth, rather than duration, is the key, and look for a “significant decline in economic activity”, using indicators such as jobless data.

Quarterly GDP data can also be subject to substantial revisions, so using monthly data from a range of sources gives a more timely view.The National Bureau of Economic Research uses business activity. Its research suggests recessions last about a year and occur after business activity peaks and starts to fall, but before it bottoms out.