RESEARCH METHOD COHEN ok

CHARACTERISTICS OF EX POST FACTO RESEARCH 267
the hypothesis. Due to lack of control of X and
other possible Xs, the truth of the hypothesized
relation between X and O cannot be asserted with
the confidence of the experimental researcher.
Basically, then, ex post facto investigations have,
so to speak, a built-in weakness: lack of control of
the independent variable or variables. As Spector
(1993: 43) suggests, it is impossible to isolate
and control every possible variable, or to know
with absolute certainty which are the most crucial
variables.
This brief comparison highlights the most important
difference between the two designs –
control. In the experimental situation, investigators
at least have manipulative control; they
have as a minimum one active variable. If an
experiment is a ‘true’ experiment, they can also
exercise control by randomization. They can assign
subjects to groups randomly; or, at the very least,
they can assign treatments to groups at random.
In the ex post facto research situation, this control
of the independent variable is not possible, and,
perhaps more important, neither is randomization.
Investigators must take things as they are and try
to disentangle them, though having said this, they
can make use of selected procedures that will give
them an element of control in this research. These
we shall touch upon shortly.
By their very nature, ex post facto experiments
can provide support for any number of different,
perhaps even contradictory, hypotheses; they
are so completely flexible that it is largely a
matter of postulating hypotheses according to
one’s personal preference. The investigator begins
with certain data and looks for an interpretation
consistent with them; often, however, a number
of interpretations may be at hand. Consider
again the hypothetical increase in road accidents
in a given town. A retrospective search for
causes will disclose half a dozen plausible ones.
Experimental studies, by contrast, begin with
a specific interpretation and then determine
whether it is congruent with externally derived
data. Frequently, causal relationships seem to be
established on nothing more substantial than
the premise that any related event occurring
prior to the phenomenon under study is assumed
to be its cause – the classical post hoc, ergo
propter hoc fallacy. 2 Overlooked is the fact that
even when we do find a relationship between two
variables, we must recognize the possibility that
both are individual results of a common third
factor rather than the first being necessarily the
cause of the second. As we have seen earlier, there
is also the real possibility of reverse causation,
e.g. that a heart condition promotes obesity rather
than the other way around, or that they encourage
each other. The point is that the evidence simply
illustrates the hypothesis; it does not test it, since
hypotheses cannot be tested on the same data from
which they were derived. The relationship noted
may actually exist, but it is not necessarily the only
relationship, or perhaps the crucial one. Before we
can accept that smoking is the primary cause
of lung cancer, we have to rule out alternative
hypotheses.
Further, a researcher may find that watching
television correlates with poor school performance.
Now, it may be there is a causal effect
here: watching television causes poor school performance;
or there may be reverse causality: poor
school performance causes students to watch more
television. However, there may be a third explanation:
students who, for whatever reason (e.g.
ability, motivation), do not do well at school
also like watching television; it may be the third
variable (the independent variable of ability or
motivation) that is causing the other two outcomes
(watching a lot of television or poor school
performance).
We must not conclude from what has just been
said that ex post facto studies are of little value;
many of our important investigations in education
and psychology are ex post facto designs. There is
often no choice in the matter: an investigator
cannot cause one group to become failures,
delinquent, suicidal, brain-damaged or dropouts.
Research must of necessity rely on existing groups.
On the other hand, the inability of ex post facto
designs to incorporate the basic need for control
(e.g. through manipulation or randomization)
makes them vulnerable from a scientific point of
view and the possibility of their being misleading
should be clearly acknowledged. Ex post facto
Chapter 12