"Doggett, David" schrieb:
>
> Dear Klazien,
>
> Intention-to-treat analysis can best be thought of in terms of compliance.
> There is no one correct way to analyze a trial; rather, one analyzes
> different ways for different purposes. If one wants to know the average
> result of applying the treatment to a population, then one uses
> intention-to-treat analysis and includes all patients initially assigned to
> the treatment or control group, regardless of whether they complied or
> dropped out or crossed over. However, this obscures the effect of treatment
> on those who comply, which is also a valuable thing to know. If I am a
> patient, I want to know what to expect from the treatment if I respond to
> treatment and comply. Averaging in a bunch of patients who don't respond or
> don't comply confounds this result.
> ....
Dear David, dear Klazien,
this specific point is more complex. As a prospective patient, I often
do not know whether I can comply with a treatment. I cannot comply,
e.g., if I develop serious side effects. And I probably will not comply
if the treatment does not work within the usual time. Most drop-outs in
studies come from these sources, only few patients drop out for reasons
unrelated to therapy (treatment of the various addictions being a
notable exception). Thus for a prospective patient, it is usually the
intent-to-treat effect size that is more meaningful. It gives the
overall chance of getting better when starting a specific treatment.
The effect size derived from patients completing the treatment is the
right choice when doing causal analyses from a pharmacological point of
view. When I want to compare the effects of two treatments or two
dosages of one treatment *independent* of possible side-effects, I take
the completer data. But these figures are of little value for the
individual patient.
Hope this addition is helpful
Rolf
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Prof. Dr. Rolf R. Engel ([log in to unmask])
Psychiatric Hospital, University of Munich
Nussbaumstr. 7, D-80336 München
Tel ..49 89 51605561, Fax ..49 89 51605562
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