Evaluating Psychological vs. Biomedical Treatments
The
elements we have described characterize what is usually termed a randomizedclinical trial (RCT), so
called because of the random assignment of participants togroups. In most ways
an RCT would be run in the same fashion for evaluating a new medication or for
evaluating a specific type of therapy. There are, however, a few differ-ences
between RCTs for drugs and RCTs for therapy.
In
evaluating biomedical treatments, we need to be alert to the possibility of placebo effects—the influence of a
patient’s beliefs and expectations in bringing abouta cure. We generally test
for placebo effects by giving the patient a medically neutral sub-stance (the
placebo); the placebo often diminishes symptoms, but because it has no active
ingredients, its effect has to be understood in terms of the patient’s beliefs:
The patient believes in the pill’s powers, and it is his faith in the
medication, not the med-ication itself, that brings the benefits.
In
the broad practice of medicine, the evidence is mixed regarding how powerful
placebos are. In some studies, placebos seem to produce real improvement
(Benson & Friedman, 1996); in others, the placebo effect is weak or
nonexistent (Hrobjartsson & Gotzsche, 2001). In the study of mental
disorders, though, we need to take the placeboeffect seriously because it is
surely plausible that a patient’s distress might be alleviated by her belief in
the cure rather than by the cure itself.
In
studies of a medication, therefore, we give the medication we are interested
in— Wellbutrin, in our example—to one group of patients, and a placebo to the
other group. This second group will receive the same attention from the
treatment staff as the Wellbutrin group, and they will be told exactly the same
things about their treatment. They will also be given the same number of pills
as the patients in the true-drug group, and on the same schedule. In this
fashion, we ensure that the two groups have the same expectations and the same
beliefs about the treatment. If we find, therefore, that the groups differ at
the end of the study, the difference must be attributed to the one element that
distinguished the two groups—the fact that the patients in one group actually
took a medication, while those in the other took inert pills.
In
principle, the same logic regarding a placebo control applies to the study of
psy-chological treatments. In practice, however, it is not clear what the
placebo would be in this case. Would we want the placebo group to work with a
therapist who listens, but without warmth? A therapist who expresses warmth,
but provides no counsel? A thera-pist who offers counsel irrelevant to the
patient’s problems? The choice between these (or other) options is not clear,
making this one source of ambiguity in interpreting RCT data for psychotherapy
(Nathan et al., 2000). For this reason, many RCTs for psychological treatments
do not have special placebo control conditions. Instead, the treatment of
interest is compared either to other standard treatments or to a wait-listcontrol. The wait-list control
is one in which participants are randomly assigned toreceive either immediate
or delayed treatment, and the immediate treatment participants’ responses to
treatment are evaluated by comparing them to the delayed treatment
participants—who have not yet started therapy.
There
is one other important way in which RCT procedures differ for psychological and
biomedical treatments. When we are testing a medicine, it is easy to ensure
that each patient gets the same number of pills and that the chemical
constituents of the pills are the same for everyone in the study. But how can
we ensure, in a study of therapy, that each patient gets the same treatment and
the same “dose”?
Investigators
usually address this point by developing a treatment manual that tells the
therapists exactly how to proceed during the study—what steps to take in
therapy, what instructions to offer, and so on. This manualized therapy denies the therapist the option of improvising
or adjusting procedures midstream, which may sometimes undermine the quality of
the therapy (Addis & Krasnow, 2000). However, this stan-dardization seems
essential if we are to assess whether a particular therapy is effective.
Clearly,
there are trade-offs associated with manualized therapy. On the positive side,
this procedure seems our best hope for learning whether a particular type of
treatment works. On the negative side, it may not accurately represent the way
that treatment would be used outside the study, since most clinicians adopt an
eclectic approach. Clinicians also often adjust their approach as the therapy
proceeds and they learn which steps seem promising for a particular individual
and which do not.
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