For teachers and students of macroeconomics.
I’m about to teach a small number of first year undergraduate students Keynesian macroeconomics, and my aim will be not to tell them that this is the macroeconomics of sticky prices. Yet I realise I’ve already gone wrong. In week one I talked about time periods in macro, and how the ‘short run’ was the length of time ‘it takes prices to fully adjust’. I must have been saying this for years. But it is at best highly misleading.
In both the New Keynesian closed economy model, and the IS/LM model, the short run is the length of time it takes the central bank to stabilise inflation (output goes to its natural rate), or less precisely to achieve full employment. For students we could equally say it is the period it takes monetary policy to achieve the real rate of interest implied by the RBC, or Classical, model. Calling this the time period it takes prices to fully adjust only makes sense when monetary policy involves some kind of nominal anchor, like a fixed money target in IS/LM. It makes no sense when monetary policy involves a central bank trying to choose the best nominal interest rate. The impact of an unexpected but subsequently known preference/demand shock, for example, would be very short lived when such a central bank knew what it was doing. (See this excellent post from Nick Rowe.)
The big danger in equating Keynesian economics with sticky prices is that students forget about the crucial role monetary policy is playing. Too many think that after an increase in aggregate demand, if contracts and menu costs were absent, higher prices would in themselves choke off the increase in aggregate demand. As they have just learnt micro, it is a natural mistake to make. They then get very confused when price flexibility does (at best) nothing at the zero lower bound.
Yet the linking of the short run with sticky prices is ubiquitous. In the edition of Mankiw I have to hand it says
“In the long run, prices are flexible and can respond to changes in supply or demand. In the short run, many prices are sticky at some predetermined level. Because prices behave differently in the short run than the long run, economic policies have different effects over different time horizons.”
This kind of statement makes sense in a fixed money supply world, but it makes much less sense in the real world. (Mankiw uses the term ‘long run’ where others would use ‘medium run’, but let us not worry about that.) Compare it with this alternative statement:
“In the long run, monetary policy adjusts to achieve steady inflation, which means output goes to its ‘natural’ or Classical level. In the short run, monetary policy fails to achieve this, so we need to look at movements in aggregate demand to explain output.”
This works for any sensible monetary policy.
In my second year lectures, I ask my students to think about a monetary policy that involved moving real interest rates in response to the output gap, but not to excess inflation. If that policy stabilised a closed economy, then what impact would the speed of price adjustment have on anything except inflation? Inflation aside, a world where price adjustment was quick would look much like a world where prices were much stickier. The ‘short run’ would have the same length, irrespective of how quickly prices adjusted.
All this is about how Keynesian economics is taught, rather than about how it is done. Yet how it is taught can also influence how it is eventually understood. One of the problems some people have with understanding that we are still in a situation of deficient demand is that it is five years after the recession ‘and surely prices should have adjusted by now’. There is also a rather more profound point. Many anti-Keynesians use this misunderstanding about price adjustment to dismiss Keynesian economics. When they say ‘I ignore Keynesian economics, because I think prices adjust rapidly’ they are really saying ‘I ignore Keynesian economics because I think monetary policy is very successful’. And in the real world, monetary policy can only be very successful by understanding Keynesian economics!