It's difficult to get a man to understand something when his after-tax salary depends on him not understanding it, to misquote Upton Sinclair.
This may explain why there's a glaring weakness in the thinking of business people, economists and politicians who see countering bracket creep and cutting the top tax rate as the key "reforms" needed to "reward hard work" and increase participation in the labour force.
Joe Hockey's repeated claim that our tax system remains much the same as it was in the 1950s is silly but, as Professor Patricia Apps, of the University of Sydney, argues in a recent paper, it's true in one important respect.
Then, our system of levying income tax on the individual, rather than the joint income of couples, fitted well with our (very Australian) system of tightly means-testing welfare benefits on the basis of family income.
Why? Because, in those days, few women continued in paid employment once they were married and, certainly, once the kids started arriving.
What's changed is a decline in the fertility rate from about 3.5 children per female to 1.9, a rise in young women's academic attainment to levels exceeding young men's, and a desire by most young mothers to return to paid employment.
Get it? Without intending to we've moved away from having the individual as the unit of taxation – a choice that scores well on both efficiency and equity – to a "quasi-joint" system of taxing families.
In consequence, when one partner – usually the father – has a full-time job, and the child-caring partner thinks about returning to paid employment, her degree of participation is discouraged not just by marginal tax rates that have risen somewhat thanks to bracket creep but, far more significantly, by the rate at which the family tax benefit is withdrawn as the wife's income is added to the husband's.
This means women deciding whether to work, and how long to work, face "effective" marginal rates of taxation far higher than the top rate of 47 per cent faced by all the executives Hockey fears will become tax exiles at any moment.
Apps demonstrates from 2010 survey figures that, before a couple's kids arrive, women, on average, work almost as many hours as men. Women's hours fall markedly when the couple has at least one child of preschool age.
That's to be expected. But Apps shows that when the average couple reaches the stage where all dependent children are of school age, mothers' hours recover to only a little more than half those of the husbands'.
The gap is only a little narrower when couples reach the stage where both parents are still of working age but have no dependent children at home.
In other words, decisions made to reduce participation in the labour force in the preschool years tend to persist even as the kids grow up.
Why could this be? Surely not because "secondary earners" (aka mothers) face effective marginal tax rates in the high double figures. If so, countering bracket creep and cutting the top rate aren't likely make much difference.
Apps' analysis goes a long way towards explaining why rates of female participation in Australia are significantly lower than in comparable countries – even New Zealand – particularly when you remember our unusually high rates of part-time female participation.
If so, she also goes a long way towards identifying the area where tax reform is likely to be most effective in encouraging work effort and participation.
Apps uses Australian data to support an empirical truth long understood by tax economists, but long forgotten by other economists and never believed by high-paid businessmen (see opening quote): the price "elasticity" (sensitivity) of labour supply is not at all high for "primary" income earners (men with full-time jobs). Other studies show much higher elasticity for "secondary" earners.
This is common sense: full-time jobs tend to come in set lumps of 38 hours or so a week, whereas mothers have far more discretion over how many hours a week they want to work. It's mainly the shift from part-time to full-time that our unintended "quasi-joint" unit of taxation is stuffing up.
There's nothing new about high effective marginal tax rates. So why do economists and their high-paid male masters keep forgetting it?
Because if they can con the pollies into cutting the top tax rate rather than fixing the means-testing of family benefits, they pay a lot less tax whether or not the "reform" encourages greater work effort in general and whether or not they personally choose to work harder or take Wednesday afternoons off for golf.
