Research methodology
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One of the most common quasi-experimental designs uses two (or more) groups, one of
which serves as a control group in which no intervention takes place. Both groups are
observed before as well as after the intervention, to test if the intervention has made any
difference. (This quasi-experimental design is called the ‘non-equivalent control group design’
because the subjects in the two groups (study and control groups) have not been randomly
assigned.)
Another type of design that is often chosen because it is quite easy to set up uses only
one
group
in which an intervention is carried out. The situation is analysed before and after the
intervention to test if there is any difference in the observed problem. This is called a
‘BEFORE-AFTER’ study. This design is considered a ‘pre-experimental’ design rather than a
‘quasi-experimental’ design because it involves neither randomisation nor the use of a control
group.
Intervention (experimental) studies can also be considered either therapeutic or
preventive
.
Therapeutic trials are conducted
among patients with a particular disease to determine the
ability of an agent or procedure to diminish symptoms, prevent recurrence, or decrease risk
of death from that disease.
A preventive trial (community trial) involves the evaluation of whether an agent or
procedure
reduces the risk of developing disease
among those
free from that condition at
enrolment. Thus, preventive trials can be conducted among individuals at usual risk (e.g.
vaccine trials)
A particular research question may be addressed using different approaches. The choice of
study design for investigation is influenced by:
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