“Prevention is better than cure,” the Prime Minister said yesterday, not once, but three times.

He has made much of the fact that currently we spend only 2% of our healthcare funding on prevention. Yesterday’s health reform report proposed a new, independent National Health Promotion and Prevention Agency and “shifting the curve” of health spending toward prevention.

In fact prevention has been fashionable for most of this decade. It is a health economist’s dream given the ageing of the population and the growth of chronic diseases: invest more now and there will be long-term payoffs in reduced hospital admissions, smaller primary care costs and greater “wellness”.

Well, maybe. But, with respect to the Prime Minister, prevention is not better than cure. Not if it costs more, and not if it costs more in terms of the overall net benefit to the patient.

There’s a body of work that suggests prevention isn’t always, or even usually, better than cure. A New England Journal of Medicine literature review last year found a huge variation in the cost-effectiveness of preventative measures (measured in cost per “quality-adjusted life-year”) and that they didn’t differ markedly from treatments in their cost-effectiveness. Some preventions and treatments led to lower overall costs. A small number actually cost more and led to poorer outcomes. The rest were in between.

Another US article teases out why this is the case. Prevention covers a huge range of measures, from advertising campaigns to encourage exercise, to screening (and frequent or less frequent screening), to vaccination and treatment for risk factors like cholesterol. They obviously vary enormously in cost — and costs can be measured in different ways. Do you count only the cost to the health funder? What about the cost to patients in time as well? A simple preventative measure like taking aspirin for heart conditions, or treatment to help smokers quit, cost little but can have big benefits or actually save money. Mass-screening programs, especially if they’re annual, are far less cost-effective. Some vaccination programs are very cost-effective for certain populations, not everyone. Cholesterol-lowering medication in certain groups yields poor results for the cost of the program.

To be fair to the Commission, it is not advocating any sort of simple shift in favour of prevention — it wants a similar evaluation framework for preventative measures compared to that used to assessing treatments.

But “shifting the curve” of health funding toward prevention means, necessarily, less funding for treatment programs. That means identifying what will receive less funding. Would you be happy to see $200m redirected from public hospitals to fund a “social marketing campaign” of TV ads encouraging people to exercise more? Especially when the ultimate effect of the campaign in terms of healthier Australians will never be known?

It’s not just coke-snorting ad executives who would benefit from a greater emphasis on prevention. There are any number of lobby groups and “research institutes”, not to mention large companies like those in the weight-loss industry, who would be only too happy to get access to an increase in preventative health funding. These people are rentseekers just like those in other industries like manufacturing who argue that the community will benefit if they get a handout. They will appear as eloquent, disinterested advocates of greater preventative health funding in debates over the Commission report, when they are anything but.

Worse, a good number of such people are ardent regulators. The behavioural change end of the preventative health spectrum has a strong whiff of social engineering about it. People who want to ban certain forms of advertising, or ban certain foods, or impose punitive taxes on sinful products, or ban urban sprawl or spend vast amounts of money on unused bike paths.

Now, before you go accusing me of being a libertarian wingnut, the problem with such advocates is not that of big government versus small government, but of the demonstrated effectiveness of such measures. A ban on advertising of junk food, while cost-free, infringes the rights of broadcasters and advertisers, and even those contemptible hypocrites should be afforded the protection of free speech; moreover, there is no evidence from places like Sweden or Quebec that such bans have any impact on obesity. Heavy investment in bike infrastructure, which does have a cost, may not translate into long-term rises in bicycling because transport choices are driven by other factors like family and work commitments.

Moreover, the costing of such measures frequently only includes the cost to taxpayers or medical funders of changed behaviour, and doesn’t include the cost in time and money to users themselves.

In short, some preventions are better than cures. Others don’t even prevent what they’re supposed to prevent. If we’re going to spend less on treatment and more on prevention, we’d better make sure we’re funding the right preventions.