## Lucas’ bridge and the Ricardian equivalence fairy-tale

18 Feb, 2015 at 19:03 | Posted in Economics | 1 Comment

Imagine a Nobel Prize winner in physics, who in public debate makes elementary errors that would embarrass a good undergraduate. Now imagine other academic colleagues, from one of the best faculties in the world, making the same errors. It could not happen. However that is exactly what has happened in macro over the last few years.

Where is my evidence for such an outlandish claim? Well here is Nobel prize winner Robert Lucas:

“But, if we do build the bridge by taking tax money away from somebody else, and using that to pay the bridge builder — the guys who work on the bridge — then it’s just a wash.  It has no first-starter effect.  There’s no reason to expect any stimulation.  And, in some sense, there’s nothing to apply a multiplier to.  (Laughs.)  You apply a multiplier to the bridge builders, then you’ve got to apply the same multiplier with a minus sign to the people you taxed to build the bridge.”

And here  is John Cochrane, also a professor at Chicago, and someone who has made important academic contributions to macroeconomic thinking:

“Before we spend a trillion dollars or so, it’s important to understand how it’s supposed to work.  Spending supported by taxes pretty obviously won’t work:  If the government taxes A by \$1 and gives the money to B, B can spend \$1 more. But A spends \$1 less and we are not collectively any better off.”

Both make the same simple error. If you spend X at time t to build a bridge, aggregate demand increases by X at time t. If you raise taxes by X at time t, consumers will smooth this effect over time, so their spending at time t will fall by much less than X. Put the two together and aggregate demand rises.

The more interesting question for me is why the errors were made … I want to suggest two answers. The first is familiarity with models. I cannot imagine anyone who teaches New Keynesian economics, or who talked to people who teach New Keynesian economics, making this mistake … The second difference between physics and macro that could lead to more mistakes in the latter is ideology … When you are arguing out of ideological conviction, there is a danger that rhetoric will trump rigour … The problem too many macroeconomists have with fiscal stimulus lies not in opposing schools of thought, or the validity of particular theories, or the size of particular parameters, but instead with the fact that it represents intervention by the state designed to improve the working of the market economy. They have an ideological problem with countercyclical fiscal policy. But the central bank is part of the state, and it intervenes to improve how the economy works, so this ideological view would also mean that you played down the role of monetary policy in macroeconomics. So ideology may also help explain a lack of familiarity with the models central banks use to think about monetary policy. In short, an ideological view that distorts economic thinking can lead to mistakes.

Simon Wren-Lewis

In case your not yet persuaded, here’s another blog post describing what goes wrong  when people like Robert Lucas and those with similar views apply their models based on Ricardian equivalence:

[T]hink about what happens when a family buys a house with a 30-year mortgage.

Suppose that the family takes out a \$100,000 home loan (I know, it’s hard to find houses that cheap, but I just want a round number). If the house is newly built, that’s \$100,000 of spending that takes place in the economy. But the family has also taken on debt, and will presumably spend less because it knows that it has to pay off that debt.

But the debt won’t be paid off all at once — and there’s no reason to expect the family to cut its spending right now by \$100,000. Its annual mortgage payment will be something like \$6,000, so maybe you would expect a fall in spending by \$6000; that offsets only a small fraction of the debt-financed purchase.

Now notice that this family is very much like the representative household in a Ricardian equivalence economy, reacting to a deficit financed infrastructure project like Lucas’s bridge; in this case the household really does know that today’s spending will reduce its future disposable income. And even so, its reaction involves very little offset to the initial spending.

How could anyone who thought about this for even a minute — let alone someone with an economics training — get this wrong? And yet as far as I can tell almost everyone on the freshwater side of this divide did get it wrong, and has yet to acknowledge the error.

Paul Krugman

Indeed — how can anyone get this wrong and make such ridiculously simple errors when arguing about fiscal stimulus?

Fiscal policy is not irrelevant. Ricardian equivalence is.

## 1 Comment

1. Exactly.

But economists are not like physicists. In physics, the theoreticians share the same labs as the experimentalists (who have the big budgets and most of the prestige). They work together to develop theory backed by empirical evidence. In economics the econometricians are weird nerds, of interest only if they can come up with data that can be tortured enough to support the economist’s pet theory. Theory without empirical support is theology; that’s most of modern economics.

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