RESEARCH METHOD COHEN ok

286 EXPERIMENTS AND META-ANALYSIS
Box 13.5
An ABAB design in an educational setting
40
Baseline
Treatment
full-session DRL
Reversal
Treatment
full-session DRL
35
Frequency of talking aloud
30
25
20
15
10
5
DRL
limit
DRL
limit
0
5 10 15 20 25 30 35
Sessions
DRL, differential reinforcement of low rates
Source:Kazdin1982
First, researchers must identify and define
the research problem as precisely as possible,
always supposing that the problem is amenable
to experimental methods.
Second, researchers must formulate hypotheses
that they wish to test. This involves making
predictions about relationships between specific
variables and at the same time making decisions
about other variables that are to be excluded from
the experiment by means of controls. Variables,
remember, must have two properties. The first
property is that variables must be measurable.
Physical fitness, for example, is not directly
measurable until it has been operationally defined.
Making the variable ‘physical fitness’ operational
means simply defining it by letting something
else that is measurable stand for it – a gymnastics
test, perhaps. The second property is that the
proxy variable must be a valid indicator of the
hypothetical variable in which one is interested.
That is to say, a gymnastics test probably is a
reasonable proxy for physical fitness; height, on
the other hand, most certainly is not. Excluding
variables from the experiment is inevitable, given
constraints of time and money. It follows therefore
that one must set up priorities among the variables
in which one is interested so that the most
important of them can be varied experimentally
while others are held constant.
Third, researchers must select appropriate levels
at which to test the independent variables. By way
of example, suppose an educational psychologist
wishes to find out whether longer or shorter periods
of reading make for reading attainment in school
settings (see Simon 1978). The psychologist will
hardly select five-hour and five-minute periods
as appropriate levels; rather, she is more likely
to choose thirty-minute and sixty-minute levels,
in order to compare with the usual timetabled
periods of forty-five minutes’ duration. In other
words, the experimenter will vary the stimuli at
such levels as are of practical interest in the reallife
situation. Pursuing the example of reading
attainment somewhat further, our hypothetical
experimenter will be wise to vary the stimuli in
large enough intervals so as to obtain measurable
results. Comparing reading periods of forty-four
minutes, or forty-six minutes, with timetabled
reading lessons of forty-five minutes is scarcely
likely to result in observable differences in
attainment.
Fourth, researchers must decide which kind of
experiment they will adopt, perhaps from the
varieties set out in this chapter.