Information Technology Reference
In-Depth Information
There is no point in conducting an experiment if you already know the
answer.
6
The use of a positive control is always to be preferred. A new
anti-inflammatory should be tested against aspirin or ibuprofen. And there
can be no justification whatever for the use of placebo in the treatment of
a life-threatening disease (Barbui et al., 2000; Djulbegovic et al., 2000).
Blind Observers
Observers should be blinded to the treatment allocation.
Patients often feel better solely because they think they ought to feel
better. A drug may not be effective if the patient is aware it is the old or
less-favored remedy. Nor is the patient likely to keep taking a drug on
schedule if he or she feels the pill contains nothing of value. She is also
less likely to report any improvement in her condition, if she feels the
doctor has done nothing for her. Vice versa, if a patient is informed she
has the new treatment, she may think it necessary to “please the doctor”
by reporting some diminishment in symptoms. These sorts of behavioral
phenomena are precisely the reason why clinical trials must include a
control.
A double-blind study in which neither the physician nor the patient
knows which treatment is received is preferable to a single-blind study in
which only the patient is kept in the dark (Ederer, 1975; Chalmers et al.,
1983; Vickers et al., 1997).
Even if a physician has no strong feelings one way or the other concern-
ing a treatment, she may tend to be less conscientious about examining
patients she knows belong to the control group. She may have other
unconscious feelings that influence her work with the patients, and she
may have feelings about the patients themselves. Exactly the same caveats
apply in work with animals and plants; units subjected to the existing, less-
important treatment may be handled more carelessly and may be less
thoroughly examined.
We recommend you employ two or even three individuals, one to
administer the intervention, one to examine the experimental subject, and
a third to observe and inspect collateral readings such as angiograms, labo-
ratory findings, and x-rays that might reveal the treatment.
Conceal Treatment Allocation
Without allocation concealment, selection bias can invalidate study results
(Schultz, 1995; Berger and Exner, 1999). If an experimenter could predict
the next treatment to be assigned, he might exercise an unconscious bias
in the treatment of that patient; he might even defer enrollment of a
6
The exception being to satisfy a regulatory requirement.
