The Belief Effect
Book review by Anthony Campbell. Copyright © Anthony Campbell
In the 1980s I quite often diagnosed patients as suffering from the
hyperventilation syndrome, which was a popular label at the time,
particularly in complementary/alternative medicine (CAM). The
physiological explanation for it was quite plausible. Patients were
supposed to have got into the habit of breathing a little too deeply,
perhaps initially owing to mild anxiety. As a result they exhaled too
much carbon dioxide with a consequent shift in blood pH towards
alkalinity. This produced numerous symptoms, including panic attacks,
cramps, tachycardia, paraesthesiae, and even convulsions. To diagnose it
we used the hyperventilation provocation test, which consisted in asking
the patient to hyperventilate for two minutes; reproduction of the
symptoms was taken to be a positive result11.
The accepted treatment of the acute attack consisted in advising the
patients to rebreathe their own air using a paper bag; for a more
lasting cure they were taught breathing exercises to favour abdominal
diaphragmatic breathing over thoracic breathing. The results were
sometimes astonishing. One woman I saw used to have attacks in which she
fell to the ground in the street and was unable to move for up to two
hours. By doing no more than explain the syndrome to her I was able to
bring about a complete cure: no further attacks. I could not have wished
for a more dramatic demonstration of the truth of the theory. But alas,
it seems I was wrong; all the evidence indicates that the
hyperventilation syndrome is a chimera. In one well-executed study the
hyperventilation provocation test showed no correlation between blood
carbon dioxide levels and patients' symptoms and it is not alone in
reaching this negative conclusion 1,6,12.
I was reminded of this in reading Dylan Evans's book, for in it he
describes a rather similar experience to mine. While working as a
psychotherapist in the 1990s he achieved an impressive cure in a patient
suffering from panic attacks by supplying a psychoanalytic explanation
for them, and he took this to be confirmatory evidence for the theory.
Now, however, he questions the cause-and-effect process that seemed so
convincing at the time. Perhaps the man's recovery was mere
coincidence, or perhaps the happy result was simply due to the patient's
belief that Evans's explanation was correct, even though it wasn't.
This is just one example of the critical approach that Evans brings to
his subject. At the outset he effectively demolishes various items of
medical folklore about the placebo effect. He makes it clear that what
we know, or think we know, about the subject is largely based on
misquotation, blind repetition of poorly substantiated claims, and the
uncritical reporting of anecdotes. We really have little firm evidence
about the matter. Although placebos are very widely used in clinical
trials, these seldom include a no-treatment group so it is impossible to
know if the improvement ascribed to the placebo might not have happened
anyway for other reasons.
In fact, researchers who have investigated placebos have produced widely
varying reports of their effectiveness, ranging from zero to 100 per
cent, though a figure of about 30 per cent is often quoted and seems to
be widely accepted. This derives from a very influential paper by Henry
Beecher published in 1955, which Evans regards as having had serious
flaws2. But Beecher was one of the leading advocates of the need to
evaluate treatments by means of randomized placebo-controlled clinical
trials, and because of this his view of the placebo as extremely
powerful became widely accepted.
Many people today believe that almost
any medical disorder you like to name may respond to a placebo, but
Evans takes this to be a medical myth. There is good evidence that
placebos can influence pain and inflammation, including peptic
ulcers, he says, and they also work for depression and anxiety, but this
is pretty much the whole of their effectiveness.
Evans uses his list of conditions that may respond to placebos to
construct a hypothesis about how they may work. In outline, he suggests
that they do so via nervous system influence on the immune system. His
idea is that they damp down the acute phase response and so produce
changes both peripherally in the tissues and centrally in the patient's
sense of well-being. He develops this idea at some length and tries to
set it in an evolutionary context to explain how it may have arisen.
This part of the book is, as he admits, somewhat speculative although
not necessarily the worse for that.
In the light of this theory I find it odd that Evans discounts the idea
that the placebo effect can apply to cancer. He tells us that there is
no evidence that placebos can cure cancer. But the medical literature
does contain a fair number of well-authenticated cases of spontaneous
remission of cancer4,5,7,8,9,11. Unless one is willing to
ascribe these to divine intervention (and not all the cases have
occurred in a religious context), there must be some physiological
explanation for them. The most popular suggestion is that such
recoveries have an immunological basis, though admittedly other
mechanisms have been suggested5,7,9. But if it is right, it
would seem to be a logical consequence of Evans's immunological
explanation of the placebo effect. His reluctance to accept this may be
due to his justifiable wish to discount over-optimistic claims that
"positive thinking" can cure cancer.
In any case, the main interest of the book, for me at least, lies not in
Evans's theorising but in his presentation of the facts about placebos
and in the implications of these facts for CAM. His view, not
surprisingly, is that all forms of "alternative medicine", as he refers
to it, depend on the placebo effect and on the patient's belief. He
assigns a central role to belief, but he makes the point that this is
not a simple concept and claims that it is possible for people to hold
beliefs without realizing it. What matters is how people behave, not
what they say, so even animals may hold beliefs of this kind.
This is a
behaviourist view of belief. "Beliefs are brain processes which cannot
be observed directly, but whose existence can usually be reliably
inferred from a person's behaviour—which includes, but is not limited
to, his verbal behaviour." In this connection he makes the important
point, which I agree with, that it is necessary for a patient to
interpret a procedure such as acupuncture as constituting a therapeutic
intervention if it is to work. Inserting needles into patients for
diagnostic as opposed to therapeutic purposes seldom seems to produce
relief of pain.
In his discussion of acupuncture he correctly points out that it is
exceedingly difficult to devise suitable control treatments for clinical
trials of it. Even single-blind trials are almost ruled out by the fact
that if they are performed by a skilled acupuncturist he or she will
know when a needle is being inserted in the "wrong" place and will
probably communicate this to the patient even without meaning to do so.
He therefore concludes that when clinical trials appear to show that
"real" acupuncture is better than "sham" acupuncture the difference is
due to inadequate blinding, and that acupuncture "is probably a pure
Whether this is true or not, acupuncture is of course a form of physical
treatment which involves a social interaction between therapist and
patient; the same is true of osteopathy and chiropractic. I agree with
Evans that the preliminary manual examination of patients must have a
therapeutic effect in itself, independently of the formal treatment
methods used, and that there is a similarity here to the grooming
behaviour of chimpanzees and other primates3.
Homeopathy is easier than acupuncture to investigate scientifically
because it is possible to provide convincing placebos for double-blind
trials. At least one meta-analysis has concluded that homeopathy is, on
average, more effective than a placebo4. Evans rejects this on the
grounds that, if homeopathy works, we must abandon most of modern
physics and chemistry, which he finds too high a price. This is really
another version of David Hume's argument against miracles. Homeopaths
will naturally object that Evans is expressing an unreasonable prejudice
here, but he is undoubtedly right in holding that research of this kind
is unlikely to settle the arguments. "Despite their appearance of
absolute impartiality and objectivity, even the most rigorous
statistical analyses allow much scope for personal interpretation and
subjective opinion." Indeed.
It is not only CAM that Evans considers to be dependent on the placebo
effect; he reaches a similar conclusion about psychotherapy. He points
out that all the numerous psychoanalytic schools and their offshoots
have about the same success rate, which suggests that their different
theoretical assumptions are irrelevant. More controversially, he adopts
much the same attitude to supposedly more scientific forms of treatment
such as cognitive and behavioural psychotherapy: even if these are
based on correct theories of how the mind works, this does not prove
that they produce their effects in the way they claim rather than by
making use of the patients' belief in their efficacy.
Perhaps the most important question of all is that taken up by Evans in
his final chapter, entitled "The Witchdoctor's Dilemma". Even if many
treatments do rely on the placebo effect for their success, does this
matter? Perhaps we should simply accept the fact and seek to maximize
the role of suggestion deliberately. We sometimes hear this argument
advanced by advocates of CAM, and it does have a good deal of validity
so far as the patient is concerned. Why should one care how one has
been made better provided one has?
But there is an obvious ethical and practical dilemma for the
practitioner. Is it ever justifiable to deceive patients, even for
their own good? And this aside, if you don't yourself believe in a
treatment, can you continue to use it effectively or will your
scepticism convey itself to your patients and inhibit the placebo
effect? Although Evans raises these questions he does not really answer
them, though he does cite the fascinating trial done in 1965 at Johns
Hopkins University, in which 15 patients suffering from anxiety were
told that they were having sugar pills yet 13 improved. The outcome of
this trial is certainly difficult to interpret for anyone who, like Evans,
regards belief as the critical element in the placebo effect,
although a possible explanation is that the patients may not really have
believed that the doctors would do anything so silly as to give anxious
people mere sugar pills and therefore concluded that they were being
lied to. As Evans remarks, this story clearly illustrates how difficult
it can be to put the principle of informed consent into practice.
This is a well-researched book that merits reading by anyone who is
seriously interested in unorthodox medicine or psychotherapy. Some may
find its conclusions unwelcome or uncomfortable. Yet although clinical
experience suggests that some complementary treatments work,
convincing objective evidence for their efficacy has frequently proved
disappointingly elusive. The fact that different versions of the various
CAM therapies all seem to have about the same success levels is also
worrying. And although it is possible to provide plausible-sounding
explanations for some forms of treatment such as acupuncture, we have to
recognize that these explanations could be wrong. For all these reasons
it is hard to exclude the possibility that much if not all of CAM works
because of the placebo effect. Whether this ultimately matters is
perhaps partly a philosophical question, but if we do in the end find
ourselves forced to conclude that these treatments work only because the
patients (and the therapists) believe in them, we shall need to confront
the difficult dilemma that Evans posits at the end of his book.
- Bass C. Hyperventilation syndrome: a chimera?. Journal of Psychosomatic
- Beecher HK. The powerful placebo. Journal of the American Medical
- Campbell A. Acupuncture and the placebo response. Complementary
Therapies in Medicine 2000;8(1):43-46.
- Heim ME, Kobele C. Spontaneous remission in cancer. Onkologie
- Hercbergs A, Leith JT. Spontaneous remission of metastatic lung cancer
following myxedema coma. Journal of the National Cancer Institute
- Hornsveld HK, Garssen B, Dop MJ, van Spiegel PI, de Haes JC.
Double-blind placebo-controlled study of the hyperventilation
provocation test and the validity of the hyperventilation syndrome.
- Kappauf H, Gallmeier WM, Wunsch PH, Mittelmeier H-O, Birkmann J,
Buschel G, Kaiser G, Kraus J. Complete spontaneous remission in a
patient with metastatic non-small-cell lung cancer. Case report, review
of literature, and discussion of possible biological pathways involved.
Annals of Oncology 1997;8(10):1031-1039).
- Kappauf HW. Unexpected benign course and spontaneous recovery in
malignant disease. Onkologie 1991;14(SUPPL. 1):32-35).
- Kleef R, Jonas WB, Knogler W, Stenzinger W. Fever, cancer incidence
and spontaneous remission. Neuroimmunomodulation 2001;9(2):55-64).
- Linde K, Clausius N, Ramirez G, Melchart D, Eitel F, Hedges LV,
Jonas WB. Are the clinical effects of homeopathy placebo effects? A
meta-analysis of placbo-controlled trials. Lancet 1997;350:834-843.
- Mastall H. Spontaneous remission of lung metastases of a primary uterus
carcinoma during immune therapy. Zeitschrift fur Onkologie
- Morgan WP. Hyperventilation syndrome: a review. American Industrial
Hygiene Association Journal 1983;44(9):685-9.
- Park L.C., Covi L. Nonblind placebo trial. Archives of General Psychiatry
- Troosters T, Verstraete A, Ramon K, Schepers R, Gosselink R,
Decramer M, Van de Woestijne KP. Physical performance of patients with
numerous psychosomatic complaints suggestive of hyperventilation.
European Respiratory Journal. 14(6):1314-9, 1999.
18 March 2003
%S The Belief Effect
%A Evans, Dylan
%G ISBN 0-00-712612-3
%P xvi + 224 pp
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