Placebo: Mind over Matter in Modern Medicine. Dylan Evans
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Название: Placebo: Mind over Matter in Modern Medicine
Автор: Dylan Evans
Издательство: HarperCollins
Жанр: Прочая образовательная литература
isbn: 9780007394265
isbn:
Nevertheless, there is a delicious irony about the search for ever greater evidential support in medicine that is behind the rise of meta-analysis. The discounting of anecdotal evidence is certainly in accord with the spirit of science. When the Royal Society, Britain’s premier scientific institution, was founded in 1662, it adopted as its motto the Latin phrase Nullius in verba – nothing by word alone. Rejecting the deference to authority that had stifled the advance of knowledge for so long, the motto nicely sums up the emphasis on experiment and observation that lies at the heart of the scientific endeavour. Yet in those days it was much simpler for scientists to observe things for themselves. There were only a handful of them, so they could all fit quite comfortably in the same room, and witness important experiments directly. It seemed as if the vagaries and Chinese whispers that beset the reliance on word of mouth had been forever vanquished. The old days, when knowledge was all about scholarship – reporting and commenting on the reports and commentaries of others – had been superseded by an insistence on first-hand observation.
Today we seem to have come full circle. The new regents of medical research can compile their meta-analyses without putting a foot outside their office, let alone actually speaking to a real patient. The papers that sit at the top of the hierarchy of evidence are works of pure scholarship, reports of reports. The ‘methods’ section contains, not a description of a laboratory procedure, but a string of terms that make up the ‘search strategy’ used to extract references to medical papers from one or more of the huge electronic databases, such as Medline, that are the present-day equivalent of the vast medieval libraries. And the conclusions of these papers must clearly be taken on trust, as it is impossible for every reader – busy consultants and harried doctors – to check the sources for himself.
Beecher’s infamous 1955 paper on the ‘powerful placebo’ is a case in point. Although lacking the sophisticated statistical apparatus of current meta-analyses, it contains the seeds of the modern idea. It collects a set of clinical trials – no mean feat in those days, when clinical trials themselves were relatively few and far between – and extracts one or two simple figures which everybody remembers. A placebo effect of 35 per cent! This astonishing figure soon became set in stone, transformed into truth by dint of repetition, quoted and requoted by hundreds of doctors who never read Beecher’s paper, let alone the studies which he reported. The experimental evidence was trumped by the word of authority, in a parody of the whole enterprise of scientific research. The founders of the Royal Society would have turned in their graves.
Chapter 2 WHAT CAN PLACEBOS REALLY DO?
Dramatic claims have been made for placebos. According to Dr Robert Buckman and Karl Sabbagh, ‘they seem to have some effect on almost every symptom known to mankind’.1 At the other extreme there are those who argue that the placebo effect is largely or even totally illusory. Arthur Shapiro, who spent forty years researching the topic from the mid-1950s until his death in 1995, concluded that there was little evidence for the view that placebos could have a direct and permanent effect on medical disorders.2 Gunver Kienle and Helmut Kiene have probed the literature on placebos in great depth and found it to be full of misquotation, blind repetition of poorly substantiated claims and the uncritical reporting of anecdotes.3 The placebo effect, they claim, is no more than a myth.
So much for the claims; what of the evidence? It is true that placebos have been used in thousands of clinical trials, but – as we saw in the last chapter – most of these studies do not include a no-treatment group. As a result, we cannot be sure that the placebo made any difference. The improvement shown by the patients in the placebo group might have occurred anyway as they recovered their health naturally, even if they hadn’t received a dummy treatment. To discover what medical conditions the placebo response can really affect, we need to look at the research much more carefully. Only if it can be shown that people with a particular condition do better when treated with a placebo than when not treated at all can we be sure that the placebo response really works for that condition.
THE POWERLESS PLACEBO
In the late 1990s, two medical researchers at the University of Copenhagen attempted to settle the debate about the placebo effect once and for all. Asbjorn Hrobjartsson and Peter Gotzsche combed through the medical literature much more extensively than anyone had done before, picking out all the studies they could find that included both a placebo group and a no-treatment group.4 They were able to identify a surprisingly large number of such trials – 130 in all. Of these, 114 provided relevant data enabling a proper comparison of the placebo group with the no-treatment group. Using meta-analysis, Hrobjartsson and Gotzsche pooled the results of these studies and concluded that, overall, there was little evidence that placebos had any powerful clinical effects.
This simple conclusion was seized on by the media and reported as proof that the placebo effect was a myth. If they had read the whole study, however, they might not have been so quick to buy Hrobjartsson and Gotzsche’s take-home message. The devil, as always, was in the details. For one thing, the studies examined by Hrobjartsson and Gotzsche fell into two distinct groups. Some had reported their results in binary terms (such as positive versus negative result), while others had used a continuous scale (such as the amount of pain relief). For the binary group, there was a small placebo effect, but the result was not significant by the normal standards of statistical research. So far, then, Hrobjartsson and Gotzsche were justified in saying that there was little evidence that placebos had any effect. For the studies using continuous measures, however, there was a significant beneficial placebo effect. These studies, then, do provide good evidence that placebos can produce clinical benefits.
Furthermore, the range of medical problems covered by the 114 studies analysed by Hrobjartsson and Gotzsche was enormous. In total, forty clinical conditions were examined, from asthma and smoking to menopause, marital discord and schizophrenia. Hrobjartsson and Gotzsche averaged over all these studies and, because there were relatively few in this sample that provided evidence in favour of the placebo effect, the negative view prevailed. But if you did the same thing for virtually any powerful drug, the result would be the same. This is because any kind of therapy that works – be it a drug, a surgical intervention or behavioural therapy – will help people with some conditions and not others. There is no such thing as a universal remedy, a real-life cure-all, a panacea.
Certainly, some people have claimed that placebos are just this. Beecher was largely responsible for floating the idea that placebos can affect virtually every medical condition. Although the evidence on which he based this claim was – as we have seen – deeply flawed, the myth of the all-powerful placebo soon became the established medical wisdom. If Hrobjartsson and Gotzsche had contented themselves with exposing this myth, the path would have been opened for a more realistic assessment of the placebo effect, distinguishing between those conditions that are placebo-responsive and those that are not. But Hrobjartsson and Gotzsche went further, asserting that there was no evidence that placebos had any effects at all.
This, at least was the upshot of their brief conclusion. In the small print, however, they were forced СКАЧАТЬ