Saturday, August 25, 2018

“Lags”: one reason economists keep getting it wrong

I’m compiling a short-list of the main things economics teaches us. One is: economic developments take longer to affect the economy than you’d expect. Economists call these delays “lags”. That there are so many of them – and their lengths keep changing – does a lot to explain why economists’ forecasts are so often wrong.

Last week Dr Luci Ellis, an assistant governor of the Reserve Bank, gave a prestigious lecture at the Australian National University devoted solely to the problem of lags.

Ellis says a lag occurs in any instance where time passes between when an activity is initiated and when it has its impact. “Almost all economic phenomena involve lags,” she says. And she’s divided them into three types.

The first is “process lags” – the time it takes for any production process to be finished. The time it takes to build a house, for instance.

This includes the time it takes to make a decision (say, about whether to build the house). Particularly where decisions are made by governments or big businesses, this can take some time. You may have to gather information, do analysis, prepare documents, convene meetings and complete review processes before you’ve decided.

Economists often compare the strengths and weaknesses of the two main instruments they use to manage the macro economy: monetary policy (the manipulation of interest rates) and fiscal policy (the manipulation of government spending and taxation in the budget).

An important difference between the two is that decisions to change interest rates can be made quickly and easily. The Reserve Bank board meets monthly, decides, has lunch and then announces its decision.

By contrast, decisions to change taxes or government spending require a lot more preparation and debate by the cabinet. Then there can be a delay of weeks or months before legislation is passed by parliament and put into effect. Sometimes the firms affected have to be given notice to prepare for the change.

The trick is, once decisions have taken effect, changes to taxes and government spending usually affect the economy more quickly than do changes in interest rates, for which the lags are “long and variable”. The full effect of a rate change could take up to three years.

Another example of decision lags is the local government approval process for building projects, which can take months.

An important case of process lag is known as the “hog cycle”. A farmer takes his pigs to market, discovers prices are high, so decides to grow more pigs.

Trouble is, this takes a few years. And pork prices have fallen back long before the pigs are ready. But when they are, the farmer still has to sell them – which depresses prices even further.

Hog cycles occur in many industries where the long delay between deciding to produce something and getting it finished means demand and supply for the product are never in sync. This causes prices to boom when demand exceeds supply, then bust when supply exceeds demand.

It’s happening now with new apartments. Demand has fallen off, but buildings begun a year or two ago are still adding to supply, putting downward pressure on prices.

The hog cycle – the long lag between rising mineral commodity prices on world markets and our new mines and gas plants finally coming on line – does much to explain the wringer the resources boom and bust has put our economy through over the past decade and a half.

Ellis’s second category is “stock-flow lags”. A stock is the amount of something at a particular point in time – say, the money in a bank account at June 30. A flow is the amounts flowing in and out of the account during a period of time. The difference between the stock at the start of a year and the stock at the end of the year will be the flows in and out.

This is important in housing, where the number of newly built homes in a year is a small fraction of the stock of all existing homes (especially after you allow for the homes that were knocked down during the year).

So if the stock of homes has fallen far short of the number of homes needed, it can take longer than you’d expect to make up the gap.

Historically, macro-economics has tended to focus on flows and ignore stock levels. But Ellis says “if you aren’t taking stocks and flows seriously you probably don’t have a realistic model of the economy”.

Her third category is “learning lags”. This is the time it takes individuals – or the whole economy – to realise economic relationships have changed and to change their behaviour accordingly.

These lags can vary because some people are quicker on the uptake than others. But also because how long it takes before you can conclude a change has occurred depends on many factors: the “noisiness of the data” (the way monthly or quarterly statistics jump around for no apparent reason) and how open you are to changing your views about how things work.

This takes us to the common case of economists having to decide whether some problem is “cyclical” (temporary) or “structural” (lasting).

Ellis says our knowledge that lags often vary in length should make us slow to conclude that the economy’s structure has changed, but human nature seems to push us the other way. It’s too easy to convince ourselves “this time is different” when usually it isn’t.

The big debate between economists at present fits this pattern: is the weakness in wage growth just the product of longer lags than we’re used to in the recovery phase, or has there been some change in workers’ bargaining power that needs correcting?

Whatever the answer, you see how ubiquitous lags are in the economy, how their length can change, how they contribute to the ups and downs of the business cycle, and how hard they make it to be sure where we are now, let alone where we’re headed.