This section contains the following:
In essence, an RCT is a study in which people are allocated at random
to receive one of two (or more) clinical interventions. Usually,
one of the interventions is regarded as a standard of comparison or
control, and the group of participants who receive it is called the
control group. The control can be conventional practice, a
placebo, or no intervention at all. The other groups are called
the ‘experimental’, ‘intervention’ or the ‘treatment’ groups.
RCTs seek to measure and compare different events that are present or
absent after the participants receive the interventions and these
events are called outcomes.
Most RCTs have a parallel design. In these studies (also called
parallel trials or RCTs with parallel group design), each group of
participants is exposed to only one study intervention. For
instance, if a group of investigators uses a parallel design to
evaluate the effects of a new analgesic compared with those of a
placebo in patients with migraine, they would give the new analgesics
to one group of patients and placebo to a different group of patients.
Most of the information in the Trial Protocol Tool relates specifically
to parallel group trials.
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This page was last updated 1st April 2005.