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The recent paper by Torgerson (10 February 2001) draws attention to
statistical considerations in the parallels between cluster randomised
controlled trials and the Zelen design. In the Zelen design, the consent
of individuals to trial entry and allocated treatment is requested AFTER
the allocation is known, and the request is usually only to those
allocated to the experimental treatment. This was predominantly to
protect the patients allocated conventional or standard treatment. In a
recent special issue of Statistics in Medicine which addressed a variety
of topics in cluster randomised controlled trials (1), one paper discusses
some ethical principles involved, mainly from a theoretical perspective
(2).
We have conducted empirical work around consent issues in this
context (3). This qualitative research was based around a conventionally
randomised trial in the UK, although other trials addressing the same
clinical question in the USA had used a Zelen design. In face to face
interviews, we asked a sample of parents of babies who had been entered
into the UK to give their views about both Zelen and non-Zelen designs.
We found that, while most parents recognised the complexity of the ethical
and practical implications of both designs, there was a marked difference
between the respondents in terms of their preferences for any future
trials. This difference was based on the treatment group to which their
children had been randomly allocated. More of the parents of children who
had been allocated to the control arm of the trial were unhappy about the
Zelen design. As this was the very group of patients the Zelen design was
trying to protect, we concluded that, at least based on this sample, the
Zelen approach should not be adopted widely without further evaluation.
This has implications for obtaining consent from individuals to
participation in the context of cluster randomised trials also, and
further empirical research is needed.
Diana Elbourne
LSHTM, London
Claire Snowdon
LSHTM, London and CFR, Cambridge
Jo Garcia
NPEU, Oxford
(1) Campbell MJ, Donner A, Elbourne DR (Eds.). Design and Analysis
of Cluster Randomized Trials. Statistics in Medicine 2001; 20 (3): 329-
496
(2) Hutton J. Are distinctive ethical principles required for
cluster randomized controlled trials? Statistics in Medicine 2001; 20
(3): 473-488
(3) Snowdon C Elbourne D, Garcia J. Zelen randomization: attitudes
of parents participating in a neonatal clinical trial. Controlled
Clinical Trials 1999; 20: 149-171
Cluster randomised controlled trials and the Zelen design
The recent paper by Torgerson (10 February 2001) draws attention to
statistical considerations in the parallels between cluster randomised
controlled trials and the Zelen design. In the Zelen design, the consent
of individuals to trial entry and allocated treatment is requested AFTER
the allocation is known, and the request is usually only to those
allocated to the experimental treatment. This was predominantly to
protect the patients allocated conventional or standard treatment. In a
recent special issue of Statistics in Medicine which addressed a variety
of topics in cluster randomised controlled trials (1), one paper discusses
some ethical principles involved, mainly from a theoretical perspective
(2).
We have conducted empirical work around consent issues in this
context (3). This qualitative research was based around a conventionally
randomised trial in the UK, although other trials addressing the same
clinical question in the USA had used a Zelen design. In face to face
interviews, we asked a sample of parents of babies who had been entered
into the UK to give their views about both Zelen and non-Zelen designs.
We found that, while most parents recognised the complexity of the ethical
and practical implications of both designs, there was a marked difference
between the respondents in terms of their preferences for any future
trials. This difference was based on the treatment group to which their
children had been randomly allocated. More of the parents of children who
had been allocated to the control arm of the trial were unhappy about the
Zelen design. As this was the very group of patients the Zelen design was
trying to protect, we concluded that, at least based on this sample, the
Zelen approach should not be adopted widely without further evaluation.
This has implications for obtaining consent from individuals to
participation in the context of cluster randomised trials also, and
further empirical research is needed.
Diana Elbourne
LSHTM, London
Claire Snowdon
LSHTM, London and CFR, Cambridge
Jo Garcia
NPEU, Oxford
(1) Campbell MJ, Donner A, Elbourne DR (Eds.). Design and Analysis
of Cluster Randomized Trials. Statistics in Medicine 2001; 20 (3): 329-
496
(2) Hutton J. Are distinctive ethical principles required for
cluster randomized controlled trials? Statistics in Medicine 2001; 20
(3): 473-488
(3) Snowdon C Elbourne D, Garcia J. Zelen randomization: attitudes
of parents participating in a neonatal clinical trial. Controlled
Clinical Trials 1999; 20: 149-171
Competing interests: No competing interests