The single best explanation for the rise of Mr Crazy, Donald Trump, is that over the four years to 2013, the real income of the top 1 per cent of American households rose by 17.4 per cent, while that of the bottom 99 per cent rose by 0.7 per cent, giving the top few 85 per cent of the growth.
Another country where the gap between high and low incomes has widened markedly is Britain. And what crazy thing have the Brit voters just gone and done? You remember.
I think it's a case of what physiotherapists call "referred pain" - what you feel in some part of your body is actually coming from a problem somewhere else.
Many voters are conscious that their income doesn't seem to be growing and know something's badly wrong. But they don't join the dots the way an economist would.
They look around for something or someone to blame. They turn against their political leaders, who are "out of touch". Which they may well be.
But, as has happened many, many times before, voters also focus their resentment on the new migrants around them, especially those of a different race or creed. These people are taking all the jobs (especially those the local don't want), or they're all unemployed and getting too much help from the government.
Australia, it turns out, has also been acting strangely of late, turning against mainstream politicians on both sides, voting for populist protectionists like the Xenophones and resurrecting Pauline Hanson and One Nation, with new improved conspiracy theories.
So what's been happening to the gap between the top and the bottom in Oz? It's been widening but, fortunately, not nearly as quickly as in the US or Britain.
The Bureau of Statistics conducts a survey of the distribution of disposable income (that is, after allowing for income tax paid and welfare benefits received) between households. It's conducted every two years and the latest was for 2013-14.
Household disposable income that year averaged $998 a week, but with households in the lowest quintile (20 per cent block) getting $375 and those in the highest quintile, $2037 a week.
It's obvious that, if income were distributed equally between all households, each 20 per cent block of households would get 20 per cent of the total income of households.
In fact, the lowest quintile's share of total income in 2013-14 was less than 8 per cent. The share of the middle quintile (those households between 10 percentage points below the median and 10 points above it) was 17 per cent.
But the highest quintile's share was 41 per cent - more than twice what they'd get if income was distributed equally.
That's proof of the wide gap between high and low incomes in Australia. It puts us above the average for income inequality among the member countries of the Organisation for Economic Co-operation and Development.
Even so, the bureau's figures show no significant worsening over the six years between 2007-08 and 2013-14 - the longest period in which its surveys can be compared on a consistent basis.
The most commonly used measure of the degree of inequality between households is the Gini coefficient - a scale running from 0, where income is equal between all households, to 1, where one household has all the income.
Our Gini was 0.34 in 2007-08 and 0.33 in 2013-14. You could call this a slight improvement, but I wouldn't - the change is too small to be taken literally.
Does that lack of change surprise you? It does me, especially as the Gini fell a little in the surveys of 2009-10 and 2011-12, before rising again in 2013-14. Huh?
Our base year of 2007-08 came just before the global financial crisis of September 2008.
Professor Peter Whiteford, of the Crawford School of Public Policy at the Australian National University, thinks the initial decline was caused by the Rudd government's big discretionary increase in pensions in 2009 and, on the other hand, the big fall in the sharemarket, which would have cut the incomes of higher income-earners.
Recessions usually hit the bottom of the distribution as well as the top by greatly increasing unemployment. But not this time because of the Rudd government's quick response and because the downturn's causes came more from the financial side of the economy.
Whiteford thinks the Gini's return to a more usual level in the latest survey is explained by the slow rise in unemployment in more recent years and the sharemarket's recovery.
But the stats bureau's practice of presenting the income distribution in quintiles tends to conceal an important development: the way income at the very top is growing much faster than it is even for people not that far from the top.
Economics professor-turned-politician Dr Andrew Leigh worked with one of the world's top experts in this field, British economist Sir Tony Atkinson, to develop a time series of movements in high incomes, based on data from the Australian Taxation Office. Leigh has handed it over to Professor Roger Wilkins, of the Melbourne Institute.
Wilkins' series shows that, between 1989 and 2013, the share of total individuals' income gained by the top 10 per cent of income-earners rose by 5 percentage points to more than 33 per cent.
But the top 5 per cent captured almost all of that increase. And the top 1 per cent claimed well over half the increase in the share of the top 5 per cent.
The top 1 per cent's share of total individuals' income is now 9 per cent. That is, their incomes average nine times what they'd be if incomes were equal.
Fortunately, this isn't nearly as extreme as it is in the US, or even Britain. But it does show Australia is moving down the same road as the others, suggesting the causes are international: technological change and globalisation.
