Dictionary of Evidence-based Medicine.pdf

Dictionary of Evidence-based Medicine 123
Figure 18 Pre-randomization consent design
participate are then randomized to receive, in a two-armed trial, the test
treatment or the control, which is chosen to be the best standard therapy
(Figure 18). In the conventional RCT, recruitment of patients is often difficult
as the need to obtain prior consent before randomization often deters
patients and doctors. Zelen suggested randomizing patients to the different
treatment groups prior to seeking consent. Such a design is referred
to as a post-randomization consent design or alternatively a pre-consent
randomization or randomized consent design. In such a trial the group
randomized to receive the best standard therapy is not bothered further
except that it is evaluated and its outcomes compared to those of the other
treatment groups. Those randomized to the treatment group are then
asked for consent to participate in the trial and be given the test treatment.
Those who agree receive it and those who refuse obtain the best standard
therapy. The outcome of the three groups can then be compared (Figure 19).
An extension of this design is the double randomized consent design in
which consent is sought from both groups after randomization (Figure 20).
The use of these randomized consent designs has caused much controversy
among ethicists, statisticians and clinical trialists. The main concern
is that proper informed consent is not obtained from at least some of the
patients although the double randomized consent design overcomes
some of this problem. Note, however, that in such trials double blinding is
not possible and introduction of substantial bias is possible (Altman DG,
Whitehead J, Parmar MKB et al. (1994) Randomized consent designs in
cancer trials. European Journal of Cancer. 31:1934-44).