BMJ  2003;327:284-285 (2 August), doi:10.1136/bmj.327.7409.284

Education and debate

Modified informed consent procedure: consent to postponed information

¹ Department of Neurology, Rudolf Magnus Institute of Neuroscience, University Medical Centre Utrecht, PO Box 85500, 3508 GA Utrecht, Netherlands, ² Julius Centre for Health Sciences and Primary Care, University Medical Centre Utrecht, ³ Department of Clinical Epidemiology and Biostatistics, Academic Medical Centre, PO Box 22660, 1100 DD Amsterdam, Netherlands

How do you obtain a valid assessment of subjective outcomes in a trial in which the participants cannot be blinded to the intervention? Bias is inevitable from unblinded patients, but trials that have not told patients about treatment in all arms have been heavily criticised. Asking participants to consent to postponed information could be a solution

The first 150 words of the full text of this article appear below.

The most powerful tool for studying the effectiveness of a medical treatment is a randomised controlled clinical trial with blinded assessment of outcomes. However, blinding is not always possible—for example, in a trial comparing a surgical intervention with non-surgical treatment or the effectiveness of supplemental care compared with conventional care. Blinding needs special attention in such studies in order to prevent bias. When outcomes are assessed by doctors, it is often easy for the assessment to be done by doctors other than those who performed the procedure. However, when studies measure patients' assessment of outcomes, blinding is much more complicated or even impossible.

Unblinded patients who assess outcomes after being informed about the different treatment options during recruitment might bias the results of a study. The likelihood of bias increases when patients have a preference for one of the treatment options. For example, patients may have been . . . [Full text of this article]

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Rapid Responses:

Read all Rapid Responses

Is modified consent ethical?

Syed Abdul Mujeeb
bmj.com, 2 Aug 2003 [Full text]

Deception equals loss of altruism

susanne stevens, et al.
bmj.com, 5 Aug 2003 [Full text]

Modified informed consent (postponed information-giving) should be allowed in some trials.

Colin J Greaves, et al.
bmj.com, 16 Dec 2003 [Full text]

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