Prerandomizations: Pros and cons.
Adam Taube
Adam.Taube@statistik.uu.se
Statistiska institutionen, Uppsala Universitet
Abstract
In a conventional randomized trial the potential participants first
get the question: Do you want to participate in the trial? If the
answer is yes, the patient is then randomized to one of two
treatment modalities and participates in the trial. An alternative
strategy was proposed in Zelen (1979) for the case when the trial is
concerned with a comparison between a new treatment (A)
and a conventional standard treatment (B): The patients are first
randomized and then those who were randomized to A get the
question: Do you want to have the new treatment A or do you prefer the
standard treatment B? (If the answer is no, they get the standard
treatment B but the results are analysed according to the intention to
treat principle). Those who have been randomized to B are not asked
about their preferences since they get the same treatment as they
would have got anyhow, had they not been included in the trial. Dr
Zelen later generalized his approach to a symmetrical design where
patients are first randomized to A or B and then asked whether they
want to accept the treatment modality they have been offered or if
they would prefer the other one. In Zelen (1992) a general theory is
given about when the conventional strategy or prerandomization is to
be prefered.
In the seminar, the prerandomization strategies will be presented
and the pros and cons of prerandomization as compared with the
conventional approach will be discussed.
References
Zelen M. (1979): A new design for randomized clinical trials.
N Eng J Med 300:1242-1245.
Zelen M. (1992): Randomized consent designs for clinical trials. An
update. Statistics in Medicine. 9:645-656.