Economic theory tells us the level of the exchange rate is an important factor in the health of the economy. Unfortunately, there's nothing in economic theory that can explain the Aussie dollar's strange behaviour in recent weeks. It's hard to know whether to cheer or boo.
We do know the Aussie has a strong and longstanding tendency to move in line with the prices we're getting for our commodity exports so, since during the past few years the prices of coal and iron ore have moved to record highs, it hasn't been surprising to see the Aussie rising to heights not seen since before it was floated in 1983.
It hit a peak of 110 US cents in early August, but seemed to settle at about 105 US cents. But in late September, during a bout of considerable anxiety on world markets about the state of the North Atlantic economies, it fell below parity, eventually getting down as low as 95 US cents.
But then this week it began going back up, reaching comfortably above parity, jumping 3 US cents in just 12 hours on Wednesday.
It's possible we've reverted to an earlier pattern where, when the global financial markets get particularly anxious about economic prospects, investors liquidate their short-term investments offshore and bring their money home to the safe haven of investment in government bonds. So the dollar appreciates (rises in value) and most other currencies depreciate (fall in value). Remarkably, this knee-jerk reaction can occur even when uncertainty about the fate of the economy is a major part of the anxiety.
That's step 1. Step 2 is for investors to calm down and start moving their money back overseas to destinations such as Australia in pursuit of higher returns than offered by bonds. If so, maybe that's what happened this week.
And if that's so, maybe step 2 has merely taken us back to square 1 - a dollar that settles well above parity. But who could be sure US cents Who knows what will happen the next time something really scary happens in Europe or the US cents Will the Aussie drop to, and stay at, a new level significantly below the 105 US cents it seemed to have settled at, or will it just go through a period of high volatility without actually changing its general level US cents
A point to note is that, though the media and markets' focus is always on our exchange rate with the greenback, economics teaches that what matters to the economy is our exchange rate with all our trading partners, not just the Americans.
Say you were taking a holiday in Britain. What would matter to you is our exchange rate with the pound. If you were going to Japan, it would be our exchange rate with the yen. In neither case would you regard our exchange rate against the greenback as particularly relevant.
It's the same story when Australian firms trade with Britain or Japan. Even if the price happens to be set in dollars - as it often is - the Aussie firm will translate that price into Aussie dollars, while the British or Japanese firm will translate it into their own currency.
Put the two together and what matters for the transaction is the Aussie-pound or Aussie-yen exchange rate. So we should be interested in our exchange rate with each of the countries with which we trade. And how much each bilateral exchange rate matters to us depends on how much trade we do with the particular country.
See where this is leading US cents The exchange rate that matters to the economy overall is the average exchange rate for all our trading partners, with each country's currency weighted according to its share of our two-way trade. Economists call this our ''effective'' exchange rate, which is represented by the trade-weighted index.
When you look at what's happened to our exchange rate against that index, you find the volatility in recent weeks is less. While we've depreciated against the greenback, we've appreciated against the euro and the Korean won.
There's always a lot of focus on what's happening to interest rates because we all know how important the rate of interest is to the strength of the economy. A rise in rates will slow economic growth by discouraging borrowing and spending; a fall in rates will hasten growth by encouraging borrowing and spending.
What's less well recognised is that the level of the exchange rate also affects the strength of the economy. So much so that the Reserve Bank brackets the two - interest rate and exchange rate - as ''monetary conditions''. When the exchange rate appreciates, this tends to slow the economy by reducing the price-competitiveness of exports and those domestically produced goods that compete against the now-cheaper imports in our domestic market.
It doesn't have much effect on domestic demand (our spending), but it does slow the growth of aggregate demand (our production - gross domestic product, in fact) by reducing exports and by diverting more of our spending into imports.
Conversely, when the exchange rate depreciates, this tends to speed the economy by improving the price-competitiveness of our export and import-competing industries. Domestic demand isn't much affected, but GDP improves because we export more, and more of our spending goes on domestically produced goods and services rather than imports.
This, of course, is why our manufacturers have been doing it tough under the high exchange rate. They've found it harder to export and to compete against imports. Though it's received far less public sympathy, our tourist industry has suffered in the same way, with fewer foreigners coming to Australia and more Aussies holidaying abroad rather than locally.
Our universities and other education exporters have been hit also.
So I'm quite sorry to see the dollar going back up this week after having fallen by up to 10 per cent from its heights. It would have been great to take a bit of the pressure off the manufacturers, tourist operators and education exporters.
The econocrats have a rule of thumb saying a sustained fall in the exchange rate of 10 per cent should lead to a rise in real GDP of about 0.75 percentage points over the following two years - say, 0.4 points in each year. (The rule also holds for a rise in the exchange rate causing slower GDP growth.)
So whereas a lasting fall in the Aussie might have been bad news for motorists (price of petrol) and people planning overseas trips, it would have helped make our multi-speed economy a little less uneven.
