I have being going over the theory behind the output gap and here is an explanation – written a few years ago. Probably not so applicable to the economic environment today
Just as Messrs Friedman and Phelps had predicted, the level of inflation associated with a given level of unemployment rose through the 1970s, and policymakers had to abandon the Phillips curve. Today there is a broad consensus that monetary policy should focus on holding down inflation. But this does not mean, as is often claimed, that central banks are “inflation nutters”, cruelly indifferent towards unemployment.
If there is no long-term trade-off, low inflation does not permanently choke growth. Moreover, by keeping inflation low and stable, a central bank, in effect, stabilises output and jobs. In the graph below the straight line represents the growth in output that the economy can sustain over the long run; the wavy line represents actual output. When the economy is producing below potential (ie, unemployment is above the NAIRU), at point A, inflation will fall until the “output gap” is eliminated. When output is above potential, at point B, inflation will rise for as long as demand is above capacity. If inflation is falling (point A), then a central bank will cut interest rates, helping to boost growth in output and jobs; when inflation is rising (point B), it will raise interest rates, dampening down growth. Thus if monetary policy focuses on keeping inflation low and stable, it will automatically help to stabilise employment and growth.
Supply side policies have the objective of raising the economy’s supply potential and in conjunction with fiscal policy can improve productivity and boost overall supply. It mainly takes the form of tax incentives, investment opportunities, and training of the labour force. It also focuses on reducing the cost burden on businesses.
The BNZ Markets Outlook produced a very interesting article on supply-side issues in the NZ economy. The graph below shows the gap between the capacity of the NZ economy against the aggregate demand. Where the line is 0 – supply = demand and there is no output gap. Above the line there is excess demand and below excess supply.
Interesting that between 2004-2007 the slowing levels of growth reflected the lack ability to increase supply into the market – approaching the inelastic part of the aggregate supply curve. This was in contrast to the official view which led us to believe that demand was slowing. With the pressure on supply, prices started to rise as did wage inflation.
The RBNZ, around 2005/06, was projecting the economy to open up some spare capacity by 2007/08. The economy actually moved into a state of greater excess demand. The difference was like failing to forecast a 4% pick-up in GDP growth.
Here is a link to the Washington Post that explains the output gap – the divide between the amount an economy can produce and what it is actually producing. Just click through the different stages of growth and see the gap widening. They also look at three growth scenarios (see image below) and the impact on the output gap.
Click here to go to the graphic.