Читать книгу Bad Science - Ben Goldacre - Страница 17

These theoretical improbabilities are interesting, but they’re not going to win you any arguments: Sir John Forbes, physician to Queen Victoria, pointed out the dilution problem in the nineteenth century, and 150 years later the discussion has not moved on. The real question with homeopathy is very simple: does it work? In fact, how do we know if any given treatment is working?

Symptoms are a very subjective thing, so almost every conceivable way of establishing the benefits of any treatment must start with the individual and his or her experience, building from there. Let’s imagine we’re talking—maybe even arguing—with someone who thinks that homeopathy works, someone who feels it is a positive experience, and who feels they get better, quicker, with homeopathy. They would say: ‘All I know is, I feel as if it works. I get better when I take homeopathy.’ It seems obvious to them, and to an extent it is. This statement’s power, and its flaws, lie in its simplicity. Whatever happens, the statement stands as true.

But you could pop up and say: ‘Well, perhaps that was the placebo effect.’ Because the placebo effect is far more complex and interesting than most people suspect, going way beyond a mere sugar pill: it’s about the whole cultural experience of a treatment, your expectations beforehand, the consultation process you go through while receiving the treatment, and much more.

We know that two sugar pills are a more effective treatment than one sugar pill, for example, and we know that salt-water injections are a more effective treatment for pain than sugar pills, not because salt-water injections have any biological action on the body, but because an injection feels like a more dramatic intervention. We know that the colour of pills, their packaging, how much you pay for them and even the beliefs of the people handing the pills over are all important factors. We know that placebo operations can be effective for knee pain, and even for angina. The placebo effect works on animals and children. It is highly potent, and very sneaky, and you won’t know the half of it until you read the ‘placebo’ chapter in this book.

So when our homeopathy fan says that homeopathic treatment makes them feel better, we might reply: ‘I accept that, but perhaps your improvement is because of the placebo effect,’ and they cannot answer ‘No,’ because they have no possible way of knowing whether they got better through the placebo effect or not. They cannot tell. The most they can do is restate, in response to your query, their original statement: ‘All I know is, I feel as if it works. I get better when I take homeopathy.’

Next, you might say: ‘OK, I accept that, but perhaps, also, you feel you’re getting better because of “regression to the mean”.’ This is just one of the many ‘cognitive illusions’ described in this book, the basic flaws in our reasoning apparatus which lead us to see patterns and connections in the world around us, when closer inspection reveals that in fact there are none.

‘Regression to the mean’ is basically another phrase for the phenomenon whereby, as alternative therapists like to say, all things have a natural cycle. Let’s say you have back pain. It comes and goes. You have good days and bad days, good weeks and bad weeks. When it’s at its very worst, it’s going to get better, because that’s the way things are with your back pain.

Similarly, many illnesses have what is called a ‘natural history’: they are bad, and then they get better. As Voltaire said: ‘The art of medicine consists in amusing the patient while nature cures the disease.’ Let’s say you have a cold. It’s going to get better after a few days, but at the moment you feel miserable. It’s quite natural that when your symptoms are at their very worst, you will do things to try to get better. You might take a homeopathic remedy. You might sacrifice a goat and dangle its entrails around your neck. You might bully your GP into giving you antibiotics. (I’ve listed these in order of increasing ridiculousness.)

Then, when you get better—as you surely will from a cold—you will naturally assume that whatever you did when your symptoms were at their worst must be the reason for your recovery. Post hoc ergo propter hoc, and all that. Every time you get a cold from now on, you’ll be back at your GP, hassling her for antibiotics, and she’ll be saying, ‘Look, I don’t think this is a very good idea,’ but you’ll insist, because they worked last time, and community antibiotic resistance will increase, and ultimately old ladies die of MRSA because of this kind of irrationality, but that’s another story.*

You can look at regression to the mean more mathematically, if you prefer. On Bruce Forsyth’s Play Your Cards Right, when Brucey puts a 3 on the board, the audience all shout, ‘Higher!’ because they know the odds are that the next card is going to be higher than a 3. ‘Do you want to go higher or lower than a jack? Higher? Higher?’ ‘Lower!’

An even more extreme version of ‘regression to the mean’ is what Americans call the Sports Illustrated jinx. Whenever a sportsman appears on the cover of Sports Illustrated, goes the story, he is soon to fall from grace. But to get on the cover of the magazine you have to be at the absolute top of your game, one of the best sportsmen in the world; and to be the best in that week, you’re probably also having an unusual run of luck. Luck, or ‘noise’, generally passes, it ‘regresses to the mean’ by itself, as happens with throws of a die. If you fail to understand that, you start looking for another cause for that regression, and you find … the Sports Illustrated jinx.

Homeopaths increase the odds of a perceived success in their treatments even further by talking about ‘aggravations’, explaining that sometimes the correct remedy can make symptoms get worse before they get better, and claiming that this is part of the treatment process. Similarly, people flogging detox will often say that their remedies might make you feel worse at first, as the toxins are extruded from your body: under the terms of these promises, literally anything that happens to you after a treatment is proof of the therapist’s clinical acumen and prescribing skill.

So we could go back to our homeopathy fan, and say: ‘You feel you get better, I accept that. But perhaps it is because of “regression to the mean”, or simply the “natural history” of the disease.’ Again, they cannot say ‘No’ (or at least not with any meaning—they might say it in a tantrum), because they have no possible way of knowing whether they were going to get better anyway, on the occasions when they apparently got better after seeing a homeopath. ‘Regression to the mean’ might well be the true explanation for their return to health. They simply cannot tell. They can only restate, again, their original statement: ‘All I know is, I feel as if it works. I get better when I take homeopathy.’

That may be as far as they want to go. But when someone goes further, and says, ‘Homeopathy works,’ or mutters about ‘science’, then that’s a problem. We cannot simply decide such things on the basis of one individual’s experiences, for the reasons described above: they might be mistaking the placebo effect for a real effect, or mistaking a chance finding for a real one. Even if we had one genuine, unambiguous and astonishing case of a person getting better from terminal cancer, we’d still be careful about using that one person’s experience, because sometimes, entirely by chance, miracles really do happen. Sometimes, but not very often.

Over the course of many years, a team of Australian oncologists followed 2,337 terminal cancer patients in palliative care. They died, on average, after five months. But around 1 per cent of them were still alive after five years. In January 2006 this study was reported in the Independent, bafflingly, as: