Structure of a Trial:
key points
i)
General structure
Patients
are allocated, by some random mechanism, to one of two, or more, treatment
groups. Outcome variable or variables
are measured on each patients and the distributions of theses variables in the
treatment groups are compared.
ii)
Eligible patients
If the nature of the patients being treated in a trial is unclear then it can
be very difficult to interpret the results of the trial. To ensure both that a) only patients of the
type you think ought to be included in the trial are actually are included, and
b) to enable clear reporting of this, all trials have eligibility criteria which define the types of patients to be
included in the trial.
iii)
Control groups
If you gave a new treatment to your patients and they got better, you would not
know if that was because of the treatment or because they would have got better
anyway. Trials (almost) always include
control groups with which to compare the new treatment. The control group can be given a) no
treatment at all, b) a dummy treatment and c) the best current treatment. (n.b.
either of a) and/or b) may be ruled out by ethical considerations)
iv)
Allocation at random
In an RCT the treatment groups are formed by randomization. This is to promote a) comparable groups, b)
eliminate (largely) predictability in treatment allocation and c) to provide a
basis for analysis.