RESEARCH METHOD COHEN ok

CO-RELATIONAL AND CRITERION GROUPS DESIGNS 265
research in reverse, for instead of taking groups that
are equivalent and subjecting them to different
treatments so as to bring about differences in
the dependent variables to be measured, an ex
post facto experiment begins with groups that are
already different in some respect and searches
in retrospect for the factor that brought about the
difference. Indeed Spector (1993: 42) suggests that
ex post facto research is a procedure that is intended
to transform a non-experimental research design
into a pseudo-experimental form.
One can discern two approaches to ex post facto
research. In the first approach one commences
with subjects who differ on an independent variable
(for example their years of study in mathematics)
and then study how they differ on the dependent
variable, e.g. a mathematics test. In a second
approach, one can commence with subjects who
differ on the dependent variable (for example
their performance in a mathematics test) and
discover how they differ on a range of independent
variables, e.g. their years of study, their liking for
the subject, the amount of homework they do in
mathematics. The ex post facto research here seeks
to discover the causes of a particular outcome
(mathematics test performance) by comparing
those students in whom the outcome is high
(high marks on the mathematics test) with
students whose outcome is low (low marks on the
mathematics test), after the independent variable
has occurred.
An example of an ex post facto piece of research
can be presented. It has been observed that staff
at a very large secondary school have been absent
on days when they teach difficult classes. An ex
post facto piece of research was conducted to try
to establish the causes of this. Staff absences on
days when teaching difficult secondary classes were
noted, as shown in the diagram.
Days when teaching difficult secondary
classes
Absences Yes No
High 26 30
Low 22 50
Total 48 80
Overall total: 128
Here the question of time was important: were the
staff absent only on days when they were teaching
difficult classes or at other times Were there other
variables that could be factored into the study, for
example age groups Hence the study was refined
further, collecting more data, as shown.
Days when
teaching difficult
secondary classes
Days when not
teaching difficult
secondary classes
Age High Low High Low
absence absence absence absence
>30 30 6 16 10
years old
30–50 4 4 4 20
years old
>50 2 2 2 28
years old
Total 36 12 22 58
Overall total: 128
This shows that age was also a factor as well as days
when teaching difficult secondary classes: younger
people are more likely to be absent. Most teachers
who were absent were under 30 years of age.
Within age groups, it is also clear that young
teachers have a higher incidence of excessive
absence when teaching difficult secondary classes
than teachers of the same (young) age group when
they are not teaching difficult secondary classes.
Of course, a further check here would be to
compare the absence rates of the same teachers
when they do and do not teach difficult classes.
Co-relational and criterion groups designs
Two kinds of design may be identified in
ex post facto research – the co-relational study
and the criterion group study. The former is
sometimes termed ‘causal research’ and the latter,
‘causal-comparative research’. A co-relational (or
causal) study is concerned with identifying the
antecedents of a present condition. As its name
suggests, it involves the collection of two sets
of data, one of which will be retrospective, with
aviewtodeterminingtherelationshipbetween
them. The basic design of such an experiment may
be represented thus: 1
Chapter 12