Sometimes causal-comparative studies are conducted solel, as
an alternative to experiments. Suppose, for example, that the curriculum
director in a large urban high school district is considering implementing a
new English curriculum. The director might try the curriculum out
experimentally, selecting a few classes at random throughout the district, and
compare student performance in these classes with comparison groups who
continue to experience the regular curriculum. This might take a considerable
amout of time, however, and be quite costly in terms of materials, teacher
preparation workshops, and so on. As an
altenative, the director might consider a causal-comparative study and compare
the achievement of students in school districts that are currently using this
curriculum with the achievement of students similar districts that do not use
the new curriculum. If the results show that students in districts (similar to
his) with the new curriculum are achieving higher scores in English, the
director would have a basisfor
going ahead and implementaing the new
curriculum in his district. Like correlational studies, causal-comparative
investigations often indentify relationship that later are studied
experimentally.
Despite their advantages, however, causal-comparative
studies do have serious limitations. The most serious lie in the lack of
control over threats to intenal validity. Since the manipulation of the
independent variable has already occurred, many of the controls we discussed in
chapter thirteen cannot be applied. Thus considerable caution must be expressed
in interpretingthe outcomes of a causal-comparative study. As with correlations
studies, relationships can be identified, but causation cannot be established.
As we have pointed out before, the alleged cause may really be an effect, the
effect may be a cause, or there may be a third variable that caused both the
alleged cause and effect.
Similarities and differences between causal-comparative and correlational research
Causal-comparative research is sometimes confused with
correlational research. Although similarities do exist, there are notable differences as well.
Similarities. Both causal-comparative and correlational
research studies are example of associational research, that is, researchers
who conduct them seek to explore relationships among variables. Both attempt to
explain phenomena of interest. Both seek to identify variables that are worthy
of later exploration through experimental research and both often provide
guidance for subsequent experimental studies. Neither permits the manipulation
of variables by the researcher, how ever.
Differences. Causal-comparative studies typically compare
two or more groups of subjects, while correlational studies require a score on
each variable for each subject. Correlational studies investigate two (or more)
quantitative variables, whereas causal-comparative studies involve at least one
categorical variable (group membership). Correlational studies analyze data using scatterplots
and/or correlation coefficients, while causal-comparative studies compare
averages or use crossbreak tables.
Similarities and differences between causal-comparative and
experimental research
Similarities. Both causal-comparative and experimental
studies typically require at least one categorical variable (group membership).
Both compare group performance (average scores) to determine relationships.
Both typically compare separate groups of subjects.
Differences. In experimental research, the independent
variable is manipulated; in causal-comparative research, no manipulation takes
place. Causal-comparative studies provide much weaker evidence for causation
than do experimental studies. In experimental research, the researcher can
sometimes assign subjects to treatment groups; in causal-comparative research,
the groups already formed- the researcher must locate them. In experimental
studies, the researcher has much greater flexibility in formulating the
structure of the desaign.
Steps involved in causal-comparative research
Problem formulation
The first step in formulating a problem in causal-comparative research is
usually to identify and define the particular phenomena of interest and then to
consider possible causes for, or consequenses of, these phenomena. Suppose, for example, that a researcher is
interested in student cereatifity. What causes creatifity? Why are a few
students highly creative while most are not? Why do some students who initially
appear to be creative seem to lose this characteristic? Why do others who at
one time are not creative later become so? And so forth.
The
researcher speculates, for example, that high-level creativity might be caused
by a combination of social failure, on the one hand, and personal recognition
for artistic or scientific achievement, on the other. The researcher also
identifies a number of alternative hypotheses that might account for a
difference between highly creative and noncreative students. Both the quantity
and quality of student’s interests, for example, might account for differences
in creatifity. Highly creative students might tend to have many diverse
interests. Parental encouragement to explore ideas might also account partly
for creatifity, as might some types of intellectual skills.
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