24 January 2010

Thinking positive

At the risk of sounding a little like a scratched record*, I had a bit of an epiphany while mulling over thoughts of homeopathy and evidence of efficacy. Homeopaths make a living by thriving on those who feel conventional medicine has, in some way, failed to cure their illness. And given there are 60 million of us in the UK alone, it only takes the tiniest of tiny minorities to supply enough anecdotes of miraculous cures to supply an entire industry. One can cite all the studies in the world about placebo, RCTs and the body's natural immunities, but personal testimony can be powerfully affecting to those considering an alternative to prescription medicine.

Mainstream science tries to counter this attack-by-anecdote through a number of arguments, most commonly by citing 'regression to the mean' - or "you would have got better anyway" as most would understand it. Impossible to prove at the individual level, it also seems unsatisfactory in dealing with the more rigorous homeopathy cure stories: where patient has pain, takes drug and feels worse and then takes homeopathic cure and leaps Lazarus-like to his feet, on top of the world. This is 'regression to the mean' + side effects of drugs - a simple enough explanation, but hardly a glowing testament to the wonders of modern medicine. But there is something else we should also consider: supposing you aren't sick at all?

I was reading about the second of the great cholera epidemics to sweep London, in 1854, when fatalities at the London Homeopathic Hospital were almost one third of those found at nearby hospitals practising conventional medicine. This is sometimes cited as evidence for homeopathy's noble and efficacious tradition - and at first sight appears impressive. Until you consider that "conventional" medicine at the time was unaware of germ theory, did not employ anti-septics and considered blood-letting as a mainstream cure for many conditions. In the usually dirty and crowded conditions, it would seem that doing nothing cleanly presented a better chance of survival than any of the leading medical interventions of the day.

This prompted me to reconsider the much trumpeted homeopathic success stories in the light of the modern version of harmful interventions: the false positive. Not even the most brilliant tests modern medicine can muster are 100% accurate. Every year a tiny proportion of people taking any number of tests will test falsely positive for a condition they don't actually have. And of course the less accurate the test, the higher the number of false positives, especially if the condition is more marginal - tests less accurate, drugs less well developed, longer term understanding of their side effects less documented. If even 0.1% of testees are false positives, that will give us a fair chunk of people every year taking drugs for a condition they don't have. And when they turn to the magic water of homeopathy, they get a miraculous "cure" and tell all their friends.

In many ways conventional medicine is a victim of its own success. The powerful demonstrations of its power and range, from the elimination of smallpox to the creation of calpol, makes people blase about its limitations, and the risks at the margins. No treatment is without risk (even homeopathy, if taken as a cure for a serious condition), and if people believe it is, they will continue to be vulnerable to quackery when they become disappointed. Public education about science and medicine needs to make people aware of this, to manage expectation and help people understand its vulnerabilities, as well as its triumphs.

* = for the under 30s a 'record' is the old word for a collection of MP3 files. A disc made from vinyl, it carried up to about 12 tracks embedded within the grooves of both its surfaces whose sounds were reproduced via a needle through amplification equipment, making it very vulnerable to damage, often in the form of getting stuck in a repeat loop of several seconds.

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