Wednesday, February 06, 2008

Micro Statistics Tutorial 02: Double Blind (Trust)

Blinding in clinical trials refers to a type of study design. The graphic explains the concept. It does not refer to the hiding of science from authors of papers, "regulators", doctors, or the public.

In a blind study, the researcher or the participant or both (double blind) are blind to (unaware of) the type of treatment being administered. Double-blind trials are more likely to produce objective findings. This is because the expectations of researcher and participant cannot alter the outcome. It also makes cheating more difficult. Practitioners of "complementary" medicine such as bone throwing are not too keen on blinded trials (bone throwing is not yet available on the NHS - but watch this space).

For a good example of blinding in practice see: Vioxx and a quacking duck

A few of us have been agonizing over the potential problem of "functional unblinding" in Vytorin/Zetia trials. This is where effective unblinding happens without officially opening the book of randomization codes. There are a few possible mechanisms for this including a) inspection of treatment surrogates or confounders, b) looking at data distributions, c) inspection of treatment side effects, or d) taking a sneak peek at the codes when no-one is looking. Each of these will form the subject of a later tutorial.

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Anonymous said...

In a large trial checking for the two "humps" in the primary outcome is unlikely to be of use, as there is so much variation in the outcome that the humps will have significant overlap. That is after all, why they are running a large trial. For example in a mortality trial for cholesterol lowering drugs those on placebo wont have obviously shorter survival.

One problem is that there can be reports produced with patients identified by a group label say A or B which may be described as unblinded. Then it is easy to work out what is happening and just one adverse event may give the true labellings.

Aubrey Blumsohn said...

I believe you are right about this potential route Ken. However we shall see. Dave the pig may also have an opinion.