>>>>>>>>>>>>>>>>>
As far as I am aware, the usual reason for conducting an open-label
trial is when blinding is considered to be either not practical or not
ethical.
However, in such cases bias is reduced by ensuring that the raw data is
analysed by people who are not aware of the identity of the comparative
treatments.
You mentioned trials evaluating insulin treatment in diabetes care but
do not provide information on what insulin treatment is being compared
with. In people with Type 1 diabetes it would not be ethical to withhold
insulin treatment and in Type 2 diabetes, if insulin treatment is being
compared with oral antidiabetic drugs than it would not be practical to
blind. If two different types of insulin are being compared, then
participants can usually guess which insulin they are allocated because
of having to calculate the appropriate insulin dose for food intake thus
introducing the possibility of bias and so on.
Does this answer your question?
With best wishes
Anjana Patel
<<<<<<<<<<<<<<<<<<<
Anjana/Ulf
Perhaps a more important source of bias is allocation concealment. There
are some great articles on this topic:
Schulz KF, Chalmers I, Hayes RJ, et al. Subverting randomization in
controlled trials. JAMA 1995;273:408-12.
Schulz KF, Grimes DA. Allocation concealment in randomised trials:
defending against deciphering. Lancet 2002;359:614-18.
Altman DG, Schulz KF. Concealing treatment allocation in randomised
trials. BMJ 2001;323:446-7.
Schulz KF, Grimes DA. Generation of allocation sequences in randomised
trials: change, not choice. Lancet 2002;359:515-9.
Torgerson DJ, Roberts C. Randomisation methods: concealment. BMJ
1999;319:375-6.
Summarised nicely here:
http://ebm.bmj.com/cgi/content/full/5/2/36
http://ebm.bmj.com/cgi/content/full/5/2/38
A good exercise (for those who learn by doing) is suggested here:
Turner T and Harris C. EBM 2006; 11: 5
http://ebm.bmj.com/cgi/content/full/11/1/5-a
It is important to realise that you can have allocation concealed
without it being a double-blind study. Allocation concealment can be a
much more important source of bias.
Also, a Anjana says, you can also have a study where the endpoints are
blinded (ie. The folks measuring the outcome don't know what the
participants were taking). The PROBE design (PRospective Open-label
Blinded Endpoint) is becoming more popular these days, but is not
without problems
So you can still have a non-blinded study (for the reasons given above)
that may be relatively free from bias provided the above is taken into
account.
Cheers (8(|)
Jonathan
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Jonathan Underhill MRPharmS
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National Prescribing Centre
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