In an interview on The Lessons of the Great Depression

So you’re not saying the New Deal was a mistake, you’re saying basically we don’t know.

One of the things I’ve been trying to do in my research is to calculate the effect, particularly on Gross Domestic Product, of government expenditure programs. And I’ve been focusing on the US experience, because that’s where I have the information, although it would be good to go beyond that. But the thing you can clearly isolate is the effect of wartime expenditure – particularly World War Two – it is so big that in a statistical sense it gives you a lot of power to figure out what is going on.

There’s both the build-up, starting in 1941, and then there’s expenditures coming down after the war, in 1945-6. There’s a lot of evidence there. Sometimes the spending in a year is 20 per cent of GDP, which is absolutely astounding. In comparison, the New Deal programs, particularly in 1934 and 1936, are only two to three per cent of GDP of extra spending.

In terms of the stuff that’s not wartime spending – which we’re probably most interested in in the current climate –it’s just hard to know from the history of the data and the time series. The New Deal is part of my research, and it’s bigger than the other non-defence expenditure in terms of stimulus, but it’s not enough to really sort it out.

So I don’t think you can reliably say what the effect is. But conceptually you’d expect the wartime spending to have a bigger effect for various reasons on the GDP than the equivalent amount of expenditure in a non-war situation. And the wartime effect you can estimate pretty precisely, and the multiplier is clearly less than one, even in World War Two – it’s in the order of 0.6, 0.7, something like that.