Tony Abbott has cut the size of the co-payment and he has excluded children and Australians on benefits, but he is insisting on a co-payment, or as he puts it a "price signal".

Like a price signal for pollution (the carbon tax) or a price signal for traffic congestion (road tolls) the theory is that if we are charged for something we'll use less of it.

Still alive: GP co-payments may be "gone" but a discretionary fee is another name for pain. Credit:Jupiterimages

But visits to the doctor aren't quite like those other things. One of the things we are buying when we go to the doctor is information - information about whether we really needed to go in the first place. We can't know until we go. Doctors and patients have what health economists call an "information asymmetry". And so that makes it entirely possible that co-payments could deter necessary, as well as frivolous, visits.

It's what the giant Rand health experiment in the United States found. It sent some people to the doctor for free, charged others small fees and others big fees. In the words of the Rand report: "Cost sharing did not seem to have a selective effect." Serious as well as trivial visits were equally discouraged and those visits that were discouraged were almost entirely first visits, those that let the patients know whether it's serious or trivial.

His move might help the budget, but it might not help public health, and there's reason to think it mightn't even help the budget as much as he thinks.

If general practitioners do find their work their work slowing down as patients are turned away by co-payments, what are they expected to do? What they are likely to do is to see other patients more intensively - to recommend follow-ups and to make their consultations last longer. They'll get less from the government per consultation (Abbott is cutting the Medicare rebate by $5 for all but young patients and concession card holders) but they are unlikely to put in fewer hours.

And these changes are unlikely to pass the Senate. Most of them are being introduced by regulations rather than legislation bypassing the need for Senate approval, but the Senate still has the ability to disallow regulations, and just last month it showed it was prepared to use it when it was presented with watered-down financial advice regulations. It isn't over yet.