Well, the placebo effect could be regression to the mean in situations where
patients are systematically reporting to doctors and entering trials on
their worse days. But this does not seem like a universal explanation for
all placebo effects.
The problem with the recent article "proving" that the placebo effect is a
"myth" is that it lumps all sorts of trials together. I don't think anyone
doubted that in some situations there is no placebo effect, and in other
situations there is. If you load up your analysis without alot of studies
for situations of serious physical problems with hard outcomes, it will
swamp out the real placebo effects in situations of milder problems more
susceptible to psychosomatic phenomena, as well as studies with soft
outcomes susceptible to subjective interpretations.
Another related issue is whether all trials need a no-treatment control
group. Again there can be no universal answer to this. Ideally all trials
would have three arms, including a no-treatment (or placebo) group, to allow
assessment of whether the active control worked properly. In laboratory
research it is standard procedure to run both negative and positive
controls. But in medical research this strategy is limited by ethical
concerns. In the many situations where the active control has established
efficacy, and no-treatment would be an undue burden on patients, then the
active control should be checked against historical results.
It is good that this study has challenged the use of placebos and no
treatment arms when they are not necessary and ethical. But the bottom line
for all these conroversies is that medical research is complicated. There
are few truly universal and simple answers. People who try to live by
simplistic truths will be right sometimes, but wrong alot. The solution is
to think each situation through carefully, and avoid blindly applying the
same research design to every situation.
David L. Doggett, Ph.D.
Senior Medical Research Analyst
Health Technology Assessment and Information Services
ECRI, a non-profit health services research organization
5200 Butler Pike
Plymouth Meeting, Pennsylvania 19462, U.S.A.
Phone: (610) 825-6000 x5509
FAX: (610) 834-1275
e-mail: [log in to unmask]
From: Ted Harding [mailto:[log in to unmask]]
Sent: Thursday, August 16, 2001 3:59 AM
To: [log in to unmask]
Subject: Re: FW: Re: Placebo effect
On 14-Aug-01 Ted Harding wrote:
> The following has just been posted to the 'allstat' list.
> In passing, I don't know what "regression to the mean"
> can have to do with it, at any rate in the usual, statistical
> sense of the term!
> -----FW: <[log in to unmask]>-----
> From: Troels Ring <[log in to unmask]>
> To: [log in to unmask]
> Subject: Re: Placebo effect
> Could it be
> Is the Placebo Powerless? An Analysis of Clinical Trials Comparing
> Placebo with No Treatment
> Hrobjartsson A., Gotzsche P. C.
> N Engl J Med 2001; 344:1594-1602, May 24, 2001.
> Best wishes
> Troels Ring, Aalborg, Denmark
> At 00:33 8/13/01, you wrote:
>>I heard something in passing lately to the effect that someone has
>>proven that the placebo effect is actually regression to the mean,
>>and otherwise doesn't exist.
> --------------End of forwarded message-------------------------
A follow-up on allstat has confirmed the NEJM reference, and also
cites a story of May 24 in New York Times, of which the following
Kolata, Gina. "Placebo Effect Is More Myth Than Science,
Study Says," New York Times, 24 May 2001, p. A20.
In a new report that is being met with a mixture of
astonishment and sometimes disbelief, two Danish researchers
say the placebo effect is a myth.
Instead, the researchers theorize, patients seem to
improve after taking placebos because most diseases have
uneven courses in which their severity waxes and wanes.
Dr. Donald Berry, for example, a statistician at the
M. D. Anderson Cancer Center in Houston, said: "I believe it.
In fact, I have long believed that the placebo effect is
nothing more than a regression effect," referring to a well-known
statistical observation that a patient who feels particularly
terrible one day will almost invariably feel better the next
day, no matter what is done for him.
On which I can only comment that this should work the other
way round as well: If one feels particularly well one day,
then one will almost invariably feel worse the next day,
no matter what is done (at least, that's my experience,
especially if the euphoria occured in the later hours of
the day before).
So it should average out -- unless of course the placebo
patients are particularly sad people ...
[And I'm still not sure that I rank this as "regression to the mean"
in the usual sense]
Best wishes to all,
E-Mail: (Ted Harding) <[log in to unmask]>
Fax-to-email: +44 (0)870 167 1972
Date: 16-Aug-01 Time: 08:59:10
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