Inefficiency resulting from individuals' over-use of GP services is much more difficult to identify. Although data shows we are going to the doctor much more often than we did 20 years ago, it is not clear how much of this growth is made up of frivolous or inappropriate use. The Australian Centre for Health Research paper provides no evidence for significant over-use but, despite this lack of data, reports persist in the media of people rushing to the doctor ''at the first sign of a sniffle''.

Complicating the argument that we are over-using GP services is robust evidence for the under-use of GP services, particularly among men and the poor. This under-use occurs in particular in the area of preventive GP services and pushes up ''downstream'' costs as untreated health problems become more serious and require more expensive care.

The challenge when introducing a GP co-payment is to set it at a level which will create a barrier to inappropriate use while not also discouraging appropriate use.

This is extraordinarily difficult in practice. If the co-payment is too low it will have no discernible impact on demand. Too high and it will create a barrier to care in the cheapest sector of the health system. Coupled with a free (at the point of service) public hospital system, the danger in setting the co-payment too high is that people may be deterred from seeking GP services and end up in the much more expensive hospital system.

If, as the paper suggests, the co-payment can be covered by private health insurance its value as a price signal would be negated completely. As poorer people are less likely to have health insurance, it would also result in the more affluent being able to access GPs without up-front costs while the most vulnerable have to stump up $5 to get in the door. In this case, the only function of the co-payment would be to increase the overall cost of our health system and to decrease its equity.