In the May budget, for instance, health spending by the federal government was forecast to swell by more than $5 billion by 2016-17, and a large part of the problem is with Medicare. Last financial year, Medicare cost $18 billion, but next financial year the bill will be nearly $21 billion. Barnes suggests that a way to slow this growth in Medicare costs is to target the GP services that Medicare funds. He estimates that if we charge bulk-billing patients $6 to visit their GP, for their first 12 visits each a year, then the government would save $750 million over a four-year period. But how does Barnes know this? Health economists like to tackle a problem like this by thinking about the doctor-patient relationship as a ''supply-and-demand'' one: they think of the doctor as the supplier of a service (the healthcare) that the patient is demanding. Then, if they are looking for ways to save money, they can try to find savings on the supply side (from the doctors) or the demand side (the patients), or both.

And Barnes' policy targets the patients (the demand side). He does so because he's going after a thing called ''moral hazard'' - the inappropriate and excessive use of a resource. As Barnes sees it, if patients can be made to think twice before going to their doctor with a minor ailment that can be treated with simple over-the-counter medications, then waiting rooms won't be clogged and doctors will be able to spend their time with people who really need help. A modest $6 fee is likely to prevent some people from going to the doctor unnecessarily, and the result will be a $750 million saving over four years. He spells it out this way: the fee would reduce demand for GP services, therefore allowing GPs to spend more time with patients who most need treatment; it would send a price signal to people who go to a doctor that GP services are not a free good; it would reduce moral hazard risks by making people think twice about going to the doctor with minor ailments; it would remind people that they have a responsibility to look after their own health rather than passing on the costs to other taxpayers; and it would reduce incentives for GPs to overservice where there are high concentrations of general practitioners. Only the last of those things targets the supply side (the doctors) of the doctor-patient relationship.

In principle, there is nothing wrong with any of those reasons. But the assumption that underpins them all is that we are rational. Barnes assumes that we will notice the $6 price signal, weigh it up against our need to see a doctor, and act accordingly (and in our best interests). But that is not how things always work. A leading expert on health inequality, Professor John Glover, has warned the Abbott government not to introduce the touted GP fee because it could have serious consequences for the sickest and poorest. Glover, who is the director of the public health information development unit at the University of Adelaide, said the fee would do little to dissuade those who see GPs too much, but it would discourage the wrong people from seeing their doctor.

He knows this because - as Fairfax's Jonathan Swan reported this week - he has led Australia's most detailed analysis on the correlation between a person's wealth and their willingness to visit a doctor. Glover says the evidence is ''very strong'' that poorer people are already under-utilising healthcare, and their rate of under-utilisation corresponds to their level of illness. By modelling a 2010 Bureau of Statistics survey of more than 15,000 households, Glover found people living in the poorest neighbourhood were more than three times more likely to delay medical consultations than those living in the wealthiest suburbs. And the reason is because of the cost. It is the only data available that tracks socio-economic status against a person's likelihood to delay visiting a doctor. Glover warned that if the government scraps Medicare bulk-billing in favour of a $6 fee, those most likely to get seriously ill would be most likely to avoid accessing preventive medicine.

We might think it's irrational to put money ahead of our health, or to stay away from the doctor if we are sick, but that's how humans behave. That's worth bearing in mind, and weighing up against the economic theory. A 2009 paper based on the Australian experience, called Out of Pocket: Rethinking Health Co-Payments by Jennifer Doggett of the Centre for Policy Development, found that small out-of-pocket fees for health services, called ''co-payments'', have had perverse effects in Australia's healthcare system, without the benefits one assumes they might have. One such effect is to make Australia one of the most high-cost out-of-pocket healthcare systems in the world. Doggett found that co-payments comprise 17 per cent of health spending in Australia, which is a higher proportion than in 13 out of 20 OECD countries. Loading Supporters of the idea have said that ''co-payments'' are nothing new in Australia's healthcare system, which is true.