Advantages Of Pretest Posttest Design

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Pretest-posttest designs grew from the simpler posttest only designs, and address some of the issues arising with assignment bias and the allocation of participants to groups.

One example is education, where researchers want to monitor the upshot of a new instruction method upon groups of children. Other areas include evaluating the furnishings of counseling, testing medical treatments, and measuring psychological constructs. The only stipulation is that the subjects must be randomly assigned to groups, in a true experimental design, to properly isolate and nullify whatever nuisance or confounding variables.

The Posttest Only Design With Non-Equivalent Control Groups

Pretest-posttest designs are an expansion of the posttest only design with nonequivalent groups, one of the simplest methods of testing the effectiveness of an intervention.

In this design, which uses 2 groups, 1 grouping is given the treatment and the results are gathered at the terminate. The command grouping receives no handling, over the same period of time, but undergoes exactly the same tests.

Statistical assay can then determine if the intervention had a pregnant effect. One mutual example of this is in medicine; i group is given a medicine, whereas the control group is given none, and this allows the researchers to determine if the drug really works. This type of design, whilst commonly using two groups, tin be slightly more than circuitous. For instance, if unlike dosages of a medicine are tested, the design can exist based effectually multiple groups.

Whilst this posttest only blueprint does find many uses, information technology is limited in scope and contains many threats to validity. It is very poor at guarding against consignment bias, considering the researcher knows nothing near the individual differences within the command group and how they may accept afflicted the outcome. Even with randomization of the initial groups, this failure to address assignment bias means that the statistical ability is weak.

The results of such a study volition always be limited in scope and, resources permitting; most researchers use a more robust design, of which pretest-posttest designs are i. The posttest only design with not-equivalent groups is ordinarily reserved for experiments performed afterwards the fact, such equally a medical researcher wishing to observe the effect of a medicine that has already been administered.

The Ii Group Control Group Pattern

This is, by far, the simplest and most common of the pretest-posttest designs, and is a useful way of ensuring that an experiment has a strong level of internal validity. The principle behind this design is relatively simple, and involves randomly assigning subjects between ii groups, a test grouping and a command. Both groups are pre-tested, and both are post-tested, the ultimate difference being that one group was administered the treatment.

Confounding Variable

This examination allows a number of distinct analyses, giving researchers the tools to filter out experimental noise and misreckoning variables. The internal validity of this design is potent, considering the pretest ensures that the groups are equivalent. The various analyses that can exist performed upon a two-group command group pretest-posttest designs are (Fig 1):

Pretest Posttest Design With Control Group

This pattern allows researchers to compare the final posttest results betwixt the ii groups, giving them an idea of the overall effectiveness of the intervention or treatment. (C)
The researcher can run into how both groups changed from pretest to posttest, whether 1, both or neither improved over time. If the control group also showed a significant comeback, then the researcher must attempt to uncover the reasons behind this. (A and A1)
The researchers can compare the scores in the two pretest groups, to ensure that the randomization process was effective. (B)

These checks evaluate the efficiency of the randomization procedure and also decide whether the grouping given the handling showed a significant difference.

Problems With Pretest-Posttest Designs

The chief trouble with this blueprint is that it improves internal validity simply sacrifices external validity to exercise so. There is no way of judging whether the process of pre-testing really influenced the results because there is no baseline measurement confronting groups that remained completely untreated. For example, children given an educational pretest may be inspired to try a little harder in their lessons, and both groups would outperform children not given a pretest, then it becomes difficult to generalize the results to encompass all children.

The other major trouble, which afflicts many sociological and educational research programs, is that information technology is impossible and unethical to isolate all of the participants completely. If two groups of children attend the same school, information technology is reasonable to presume that they mix exterior of lessons and share ideas, potentially contaminating the results. On the other paw, if the children are drawn from different schools to prevent this, the risk of selection bias arises, considering randomization is not possible.

The two-group command group design is an uncommonly useful research method, as long as its limitations are fully understood. For extensive and specially important enquiry, many researchers utilize the Solomon iv group method, a design that is more costly, simply avoids many weaknesses of the uncomplicated pretest-posttest designs.