RESEARCH METHOD COHEN ok

278 EXPERIMENTS AND META-ANALYSIS
and then to focus only on certain ones of these
is to miss synergy and the spirit of the whole.
Measurement, however acute, may tell us little of
value about a phenomenon; I can measure every
physical variable of a person but the nature of the
person, what makes that person who she or he is,
eludes atomization and measurement. Randomized
controlled trials belong to a discredited view of
science as positivism.
Though we address ethical concerns in
Chapter 2, it is important here to note the
common reservation that is voiced about the twogroup
experiment (e.g. Gorard 2001: 146), which
is to question how ethical it is to deny a control
group access to a treatment or intervention in
order to suit the researcher (to which the counterargument
is, as in medicine, that the researcher
does not know whether the intervention (e.g.
the new drug) will work or whether it will bring
harmful results, and, indeed, the purpose of the
experiment is to discover this).
The two control groups and one
experimental group pretest-post-test
design
This is the Solomon (1949) design, intended to
identify the interaction effect that may occur if
the subject deduces the desired result from looking
at the pretest and the post-test. It is the same
as the randomized controlled trial above, except
that there are two control groups instead of one.
In the standard randomized controlled trial any
change in the experimental group can be due to
the intervention or the pretest, and any change
in the control group can be due to the pretest.
In the Solomon variant the second control group
receives the intervention but no pretest. This can
be modelled thus:
Experimental RO 1 X O 2
Control 1 RO 3 O 4
Control 2 X O 5
Thus any change in this second control group
can be due only to the intervention. We refer
readers to Bailey (1994: 231–4) for a full explication
of this technique and its variants (see
http://www.routledge.com/textbooks/
9780415368780 – Chapter 13, file 13.4. ppt).
The post-test control and experimental
group design
Here participants are randomly assigned to a
control group and an experimental group, but there
is no pretest. The experimental group receives
the intervention and the two groups are given
only a post-test (see http://www.routledge.com/
textbooks/9780415368780 – Chapter 13, file 13.5.
ppt). The design is:
Experimental R 1 X O 1
Control R 2 O 2
The post-test two experimental groups
design
Here participants are randomly assigned to
each of two experimental groups. Experimental
group 1 receives intervention 1
and experimental group 2 receives intervention
2. Only post-tests are conducted on
the two groups (see http://www.routledge.com/
textbooks/9780415368780 – Chapter 13, file 13.6.
ppt). The design is:
Experimental 1 R 1 X 1 O 1
Experimental 2 R 2 X 2 O 2
The pretest-post-test two treatment
design
Here participants are randomly allocated to
each of two experimental groups. Experimental
group 1 receives intervention 1 and
experimental group 2 receives intervention
2. Pretests and post-tests are conducted to
measure changes in individuals in the two
groups (see http://www.routledge.com/textbooks/
9780415368780 – Chapter 13, file 13.7. ppt). The
design is:
Experimental 1 RO 1 X 1 O 2
Experimental 2 RO 3 X 2 O 4
The true experiment can also be conducted
with one control group and two or more experimental
groups. (see http://www.routledge.com/