RESEARCH METHOD COHEN ok

270 EX POST FACTO RESEARCH
(and also the causal model), however, the independent
variable is beyond her control, having
already occurred. It may therefore be described in
this design as non-manipulable.
Procedures in ex post facto research
Ex post facto research is concerned with discovering
relationships among variables in one’s data; and
we have seen how this may be accomplished
by using either a causal or causal-comparative
model. We now examine the steps involved in
implementing a piece of ex post facto research.
We may begin by identifying the problem
area to be investigated. This stage will be
followed by a clear and precise statement of
the hypothesis to be tested or questions to be
answered. The next step will be to make explicit
the assumptions on which the hypothesis and
subsequent procedures will be based. A review of
the research literature will follow. This will enable
the investigator to ascertain the kinds of issues,
problems, obstacles and findings disclosed by
previous studies in the area. There will then follow
the planning of the actual investigation and this
will consist of three broad stages – identification
of the population and samples; the selection and
construction of techniques for collecting data; and
the establishment of categories for classifying the
data. The final stage will involve the description,
analysis and interpretation of the findings.
It was noted earlier that the principal weakness
of ex post facto research is the absence of control
over the independent variable influencing the dependent
variable in the case of causal designs or
affecting observed differences between dependent
variables in the case of causal-comparative designs.
Although ex post facto researchers are denied not
only this kind of control but also the principle of
randomization, they can nevertheless utilize procedures
that provide some measure of control in
their investigation; it is to some of these that we
now turn.
One of the commonest means of introducing
control into this type of research is that
of matching the subjects in the experimental
and control groups where the design is
causal-comparative. Ary et al. (1972) indicate
that matched pair designs (see Chapter 13) are
careful to match the participants on important and
relevant characteristics that may have a bearing
on the research.
There are difficulties with this procedure,
however, for it assumes that the investigator knows
what the relevant factors are, that is, the factors
that may be related to the dependent variable.
Further, there is the possibility of losing those
subjects who cannot be matched, thus reducing
one’s sample.
As an alternative procedure for introducing
adegreeofcontrolintoex post facto research,
Ary and his colleagues (1972) suggest building
the extraneous independent variables into the
design and then using an analysis of variance
technique. For example, if intelligence is a relevant
extraneous variable but it is not possible to
control it through matching or other means, then
it could be added to the research as another
independent variable, with the participants being
classified in terms of intelligence levels. Through
analysis of variance techniques the dependent
variable measures would then be analysed and this
would reveal the main and interaction effects of
intelligence, indicating any statistically significant
differences between the groups on the dependent
variable, even though no causal relationship
between intelligence and the dependent variable
could be assumed.
Yet another procedure which may be adopted
for introducing a measure of control into ex post
facto design is that of selecting samples that are
as homogeneous as possible on a given variable.
For example, Ary et al. (1972) suggest that if
intelligence were a relevant extraneous variable,
its effects could be controlled by including
participants from only one intelligence level.
This would disentangle the independent variable
from other variables with which it is commonly
associated, so that any effects found could
be associated justifiably with the independent
variable.
Finally, control may be introduced into an ex
post facto investigation by stating and testing any
alternative hypotheses that might be plausible