Jumat, 20 Juli 2012

causal-comparative research

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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