The biggest economic story last week wasn't all the wishful thinking about raising the goods and services tax, it was Reserve Bank governor Glenn Stevens' warning that the economy's "potential" rate of growth may be lower than we've assumed.
Predictably, those commentators who did see the significance of this news were too busy putting their own spin on it to make sure what Stevens' said was widely taken in. So let me have a go.
The macro managers' long-standing belief that the economy's "trend" rate of growth is 3 per cent a year or a fraction more has been challenged by the Bureau of Statistics' labour force estimates showing that, over the past year, the rate of unemployment has stabilised at 6 per cent.
Trouble is, the latest national accounts show the economy growing by only 2.3 per cent over the year to March. This is well below the trend rate that, almost by definition, is the rate at which the economy must grow to hold the unemployment rate steady.
How is this discrepancy explained? Stevens ran through the range of possibilities. Maybe employment hasn't been growing as strongly as the figures say at present. Maybe the economy has been growing more strongly than the figures say at present.
Or maybe part of the surprisingly strong growth in employment is explained by the unusually slow growth in wage rates, which would be saving some jobs and creating others.
The final possibility – and the one to which Stevens gives most weight – is that the trend rate of growth is lower than we've assumed, thus allowing unemployment to stabilise at a lower rate of economic growth than we've assumed.
Economists use the term "trend" in both a backward-looking and a forward-looking sense. If you calculate our average actual rate of growth over the past 10 or 20 years, this must have been our "potential" growth during that period.
If nothing in the economy has changed over that time, it should also be our average, trend rate of growth in the coming five or 10 years.
However, things do change – the population ages, for instance – so economists have to make guesses about what our potential growth rate will be in the future.
Our potential growth rate is the maximum rate at which the economy can grow on average over the medium term without a causing a serious inflation problem. It's set by the economy's supply side.
It represents the average rate at which the economy's capacity to produce goods and services is growing. And this is usually thought of as being determined by the rate of growth in the working population plus the rate of improvement in the productivity of labour.
(Whether in any particular year the economy is growing at a rate below, at or above its potential growth rate is determined by the strength of demand at the time. However, the economy can grow faster than its potential "speed limit" only for as long as it has idle production capacity to use up.)
But this is where those commentators who cottoned on to the significance of Stevens' views jumped to their own conclusions about what was causing the suspected slowdown in potential growth. They assumed it must be caused by a slowdown in labour productivity improvement.
Why? Because this fits well with the economists' (including Stevens') long-running campaign to persuade us to undertake more micro-economic reform so as to raise productivity and, hence, material living standards.
What they missed in their missionary zeal was Stevens' clear indication that he thought the culprit was slower-than-expected population growth.
The econocrats' figuring suggest a potential growth rate of 3 per cent would be explained by population growth of 1.7 per cent to 1.8 per cent a year, plus growth in labour productivity of 1.2 per cent to 1.3 per cent a year.
So their expected rate of productivity improvement is already pretty low, while the end of the mining construction boom and slow growth generally have seen population growth slow to 1.5 per cent a year or less as the net intake of workers on temporary 457 visas falls and Kiwis go home to a faster-growing economy.
The other thing the missionaries missed was Stevens point that, to the extent the lower trend rate is caused by lower population growth, it shouldn't involve any slower rate of improvement in our material living standards, as measured by growth per person.
Missionary micro-economic reformers won't win lasting converts by misrepresenting our present position, nor the outlook for growth. Their pessimism about future productivity improvement isn't supported by our more recent performance. It's little more than a guess.
