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Number of Intervention
Groups
Over half of the published
RCTs on occlusal splints have included three or more groups. Although
more than two groups can be valuable, seasoned investigators advise
that RCT planners should proceed cautiously into this realm (Green,
2002).
Oftentimes including
an additional group is overly ambitious and mainly serves to dilute
the already scarce resources for the main two groups. It is critical
to determine if the additional group will add to overall aim and
scientific question at hand. Most prior TMD trials have been underpowered,
and adding a third group was undoubtedly a contributing factor
to this for many of them.
If resources are not
unduly limited, multi-arm trials or factorial designs can efficiently
answer more than one scientific question. An example of a factorial
design would include four groups:
- A
control group of usual TMD treatment
- A
group of usual treatment plus group counseling sessions
- A
group of usual treatment plus a muscle relaxant medication
- A group of usual
treatment plus muscle relaxant and group counseling
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