Assessment:
key points
i)
Double and single blindness
The
assessment of an outcome variable may be affected if the person making the
assessment knows which treatment the patient has received. The response to certain types of question, e.g.
those relating to more subjective matters such as quality of life, can also be
affected if the patient knows which treatment has been allocated. Trials in which the patient does not know
which treatment has been assigned are known as single blind. Trials in which neither patient nor the
assessing/treating doctor does not know the assignment are double-blind.
ii)
Placebos
Treatments,
almost always tablets, which look like the active preparation but which contain
no active ingredient, are known as placebos.
Placebos have two main uses.
First they can be used to take account of the ‘placebo’ effect, in which
the condition of a patients might be affected simply by the act of taking a
tablet, or of feeling that something is being done for them, irrespective of
the possible effect of the active ingredient.
Second, they can be important in ensuring that a trial can be run with
appropriate blinding.
(a
BBC radio programme giving a lay overview of the ‘Placebo effect’ can be found here: the item starts about one and a half minutes
into the programme)