Experimental
Design Overview
Pretest Posttest
Control Group
Posttest Only
Control Group
Solomon Four
Group
Static Group
Comparison
Nonequivalent
Control Group
Counterbalanced
Time-Series
Purpose
Demonstrates a
casual
relationship
between two
variables.
If the pretest will
have an affect on
the independent
variable or there
is no valid
pretest measure.
Cannot be
certain of initial
equivalence of
groups.
Random sample
from population.
Random
assignment to
experimental &
control groups.
1. Introduce
independent
variable
2. Measure the
dependent
variable
Offers greatest
amount of
experimental
control. Requires
the most effort
(2x2 factorial).
Two groups get
pretest (control
& experimental)
and two do not.
Random sample
from population.
Random
assignment to
one of four
conditions.
1. Measure the
dependent
variable (2/4)
2. Introduce
independent
variable
3. Measure the
dependent
variable
Same as Posttest
Only Control
Group with
naturally
assembled
groups.
Lack of pretest
without random
sampling of
participants.
Two naturally
assembled
experimental
and control
groups as similar
as possible.
1. Introduce
independent
variable
2. Measure the
dependent
variable
Same as Pretest
Posttest Control
Group with
naturally
assembled
groups.
Lack of random
sampling of
participants.
Independent
variables
introduced in
different orders.
Used when cannot
randomly sample.
Lack of random
sampling of
participants.
One group with
multiple
measurements of
dependent
before and after
experiment
Two naturally
assembled
experimental
and control
groups as similar
as possible.
1. Measure the
dependent
variable
2. Introduce
independent
variable
3. Measure the
dependent
variable
Two naturally
assembled groups
as similar as
possible.
One naturally
assembled
group.
1. Measure the
dependent
var (multiple
times)
2. Introduce
independent
variable
3. Measure the
dependent
var (multiple
times)
Analysis of
Covariance
(ANCOVA).
Compare
posttest mean
scores of the two
groups with
pretest scores
used as a
covariate.
Controlled
Controlled
Controlled
t test comparing
means of groups.
t test comparing
means of groups.
Analysis of
variance
(ANOVA) for
more than two
groups studied.
ANCOVA if
other variables.
Controlled
Controlled
Controlled
Analysis of
variance
(ANOVA). Any
significant main
and interaction
effects of vars
are explored
using a post hoc
analysis such as
the Scheffe test.
Controlled
Controlled
Controlled
Analysis of
variance
(ANOVA) for
more than two
groups studied.
ANCOVA if
other variables.
Possible concern
Possible concern
Possible concern
Analysis of
Covariance
(ANCOVA).
Compare
posttest mean
scores of the two
groups with
pretest scores
used as a
covariate.
Controlled
Controlled
Controlled
1. Measure the
dependent var
2. Introduce
independent
var (G1)
3. Measure the
dependent var
4. Introduce
independent
var (G2)
5. Measure the
dependent var
Repeated measure
of analysis of
variance
(ANOVA).
Repeated analysis
eliminates
differences
between
participants from
experimental error
Controlled
Controlled
Possible concern
Controlled
Controlled
Controlled
Controlled
Controlled
Possible concern
Controlled
Controlled
Controlled
Controlled
Controlled
Possible concern
Controlled
Controlled
Controlled
Controlled
Controlled
Possible concern
Controlled
Possible concern
Controlled
Controlled
Controlled
Possible concern
Possible concern
Controlled
Controlled
Controlled
Controlled
Possible concern
Controlled
Controlled
Controlled
Controlled
Controlled
Controlled
Controlled
Controlled
Controlled
Controlled
Controlled
Not applicable
Possible concern
Possible concern
Possible concern
Possible concern
Possible concern
Possible concern
Possible concern
Possible concern
Possible concern
Possible concern
Controlled
Controlled
Not applicable
Not applicable
Possible concern
Possible concern
Possible concern
Possible concern
Possible concern
Controlled
Not applicable
Possible concern
Possible concern
Possible concern
Concern
Concern
Concern
Concern
Possible concern
Possible concern
Possible concern
Concern
Concern
Concern
Concern
Possible concern
Possible concern
Possible concern
Possible concern
Possible concern
Possible concern
Possible concern
Controlled
Controlled
Controlled
Controlled
Controlled
Controlled
Controlled
Controlled
Controlled
Controlled
Controlled
Controlled
Possible concern
Controlled
Controlled
Possible concern
Possible concern
Controlled
Possible concern
Controlled
Possible concern
Controlled
Possible concern
Possible concern
Controlled
Possible concern
Controlled
Controlled
Possible concern
Controlled
Possible concern
Controlled
Possible concern
Possible concern
Controlled
Possible concern
Possible concern
Controlled
Possible concern
Possible concern
Possible concern
Controlled
Controlled
Possible concern
Controlled
Controlled
Controlled
Controlled
Possible concern
Possible concern
Possible concern
Possible concern
Possible concern
Possible concern
Possible concern
Possible concern
Possible concern
Possible concern
Possible concern
Possible concern
Possible concern
Possible concern
Possible concern
Miscellaneous or
Weaknesses
Sampling
Steps
Analysis of Data
Maturation
Selection
Selection by
maturation interaction
Statistical regression
Mortality
Instrumentation
Testing
History
Resentful
demoralization of the
control group
Diffusion of treatment
Compensatory rivalry
by the control group
Compensatory
equalization
Generalization across
participants
Interaction of
personological vars
Verification of
independent variable
Multiple treatment
interference
Novelty and
disruption effects
Hawthorne effect
Experimenter effects
Pretest sensitization
Posttest sensitization
Interaction of time of
measurement and
treatment effects
Measurement of the
dependent variable
Interaction of history
and treatment effects
Random sample
from population.
Random
assignment to
experimental &
control groups.
1. Measure the
dependent
variable
2. Introduce
independent
variable
3. Measure the
dependent
variable
Graphical visual
analysis,
multiple
regression and/
or log linear
analysis.
Controlled
Controlled
Controlled