RESEARCH METHOD COHEN ok

13
Experiments, quasi-experiments, single-case
research and meta-analysis
Introduction
The issue of causality and, hence, predictability has
exercised the minds of researchers considerably
(Smith 1991: 177). One response has been in the
operation of control, anditfindsitsapotheosis
in the experimental design. If rival causes or
explanations can be eliminated from a study
then clear causality can be established; the model
can explain outcomes. Smith (1991: 177) claims
the high ground for the experimental approach,
arguing that it is the only method that directly
concerns itself with causality; this, clearly is
contestable, as we make clear in Part Three of
this book.
In Chapter 12, we described ex post facto
research as experimentation in reverse in that ex
post facto studies start with groups that are already
different with regard to certain characteristics and
then proceed to search, in retrospect, for the
factors that brought about those differences. We
then went on to cite Kerlinger’s description of the
experimental researcher’s approach:
If x, theny; iffrustration,thenaggression... the
researcher uses some method to measure x and then
observes y to see if concomitant variation occurs.
(Kerlinger 1970)
The essential feature of experimental research
is that investigators deliberately control and
manipulate the conditions which determine the
events in which they are interested, introduce
an intervention and measure the difference that
it makes. An experiment involves making a
change in the value of one variable – called
the independent variable – and observing the
effect of that change on another variable – called
the dependent variable. Using a fixed design,
experimental research can be confirmatory, seeking
to support or not to support a null hypothesis,
or exploratory, discoveringtheeffectsofcertain
variables. An independent variable is the input
variable, whereas the dependent variable is the
outcome variable – the result; for example, Kgaile
and Morrison (2006) indicate seven independent
variables that have an effect on the result (the
effectiveness of the school) (Box 13.1).
In an experiment the post-test measures the
dependent variable, and the independent variables
are isolated and controlled carefully.
Imagine that we have been transported to a
laboratory to investigate the properties of a new
wonder-fertilizer that farmers could use on their
cereal crops, let us say wheat (Morrison 1993:
44–5). The scientist would take the bag of wheat
seed and randomly split it into two equal parts.
One part would be grown under normal existing
conditions – controlled and measured amounts
of soil, warmth, water and light and no other
factors. This would be called the control group.
The other part would be grown under the same
conditions – the same controlled and measured
amounts of soil, warmth, water and light as the
control group, but, additionally,thenewwonderfertilizer.
Then, four months later, the two groups
are examined and their growth measured. The
control group has grown half a metre and each ear
of wheat is in place but the seeds are small. The
experimental group, by contrast, has grown half
ametreaswellbuthassignificantlymoreseeds
on each ear, the seeds are larger, fuller and more
robust.