In this design, a single test group or area is selected and the dependent variable is measured before introduction of the treatment.
Informal
Experimental Designs
Before
and after without control design:
In this design, a single test
group or area is selected and the dependent variable is measured before
introduction of the treatment. Then the treatment is introduced and the
dependent variable is measured again after the treatment has been introduced.
The effect of the treatment would be equal to the level of the phenomenon after
the treatment minus the level of the phenomenon before the treatment. Thus, the
design can be presented in the following manner:
The main difficulty of such a design is that with the passage of time
considerable extraneous variations may be there in its treatment effect. After-only
with control design:
Two groups or areas are selected
in this design and the treatment is introduced into the test area only. Then
the dependent variable is measured in both the areas at the same time.
Treatment impact is assessed by subtracting the value of the dependent variable
in the control area from its value in the test area. The design can be
presented in the following manner:
The basic assumption in this type
of design is that the two areas are identical with respect to their behavior
towards the phenomenon considered. If this assumption is not true, there is the
possibility of extraneous variation entering into the treatment effect. Before
and after with control design:
In this design, two areas are
selected and the dependent variable is measured in both the areas for an
identical time-period before the treatment. Thereafter, the treatment is
introduced into the test area only and the dependent variable is measured in both for and
identical time – period after the introduction of the treatment. The effect of
the treatment is determined by subtracting the change in the dependent variable
in the control area from the change in the dependent variable in test area.
This design can be shown in the following way:
This design is superior to the
previous two designs because it avoids extraneous variation resulting both from
the passage of time and from non-comparability of the rest and control areas.
But at times, due to lack of historical data time or a comparable control area,
we should prefer to select one of the first two informal designs stated above.
Tags : Research Methodology - Experiments
Last 30 days 8811 views