Pretest–Posttest Design Show
The basic premise behind the pretest–posttest design involves obtaining a pretest measure of the outcome of interest prior to administering some treatment, followed by a posttest on the same measure after treatment occurs. Pretest–posttest designs are employed in both experimental and quasi-experimental research and can be used with or without control groups. For example, quasi-experimental pretest–posttest designs may or may not include control groups, whereas experimental pretest–posttest designs must include control groups. Furthermore, despite the versatility of the pretest–posttest designs, in general, they still have limitations, including threats to internal validity. Although such threats are of particular concern for quasi-experimental pretest–posttest designs, experimental pretest–posttest designs also contain threats to internal validity. Types of Pretest–Posttest Designs without Control GroupsOne-Group Pretest-Posttest DesignIn the simplest pretest–posttest design, researchers gather ... locked icon Sign in to access this contentSign in Get a 30 day FREE TRIAL
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Pretest SensitizationPretest sensitization refers to the potential or actuality of a pretreatment assessment's effect on subjects in an experiment. The term has different meanings in various disciplines. In medicine and biology, it typically refers to a physical reaction to an initial administration of a drug or regimen. In the social sciences, it has come to mean a cognitive or psychological change in a subject due to administration of a test or observation of the subject. Although the mechanism of sensitization is typically not investigated or even known, the effect on behavior or response has been long documented. This is referred to here as the pretest effect. This entry focuses on the research of this phenomenon, methods of evaluation, and related statistical considerations. ResearchPretest effects have been of ... locked icon Sign in to access this contentSign in Get a 30 day FREE TRIAL
sign up today! To make things easier, the following will act as representations within particular designs:
The three experimental designs discussed in this section are: The One Shot Case StudyThis is a single group studied only once. A group is introduced to a treatment or condition and then observed for changes which are attributed to the treatmentX O The Problems with this design are:
One Group Pre-Posttest DesignThis is a presentation of a pretest, followed by a treatment, and then a posttest where the difference between O1 and O2 is explained by X:O1 X O2 However, there exists threats to the validity of the above assertion:
The Static Group ComparisonThis is a two group design, where one group is exposed to a treatment and the results are tested while a control group is not exposed to the treatment and similarly tested in order to compare the effects of treatment.Threats to validity include:
The next three designs discussed are the most strongly recommended designs: The Pretest-Posttest Control Group DesignThis designs takes on this form:This design controls for all of the seven threats to validity described in detail so far. An explanation of how this design controls for these threats is below.
The factors described so far effect internal validity. These factors could produce changes which may be interpreted as the result of the treatment. These are called main effects which have been controlled in this design giving it internal validity. However, in this design, there are threats to external validity (also called interaction effects because they involve the treatment and some other variable the interaction of which cause the threat to validity). It is important to note here that external validity or generalizability always turns out to involve extrapolation into a realm not represented in one's sample. In contrast, internal validity are solvable within the limits of the logic of probability statistics. This means that we can control for internal validity based on probability statistics within the experiment conducted, however, external validity or generalizability can not logically occur because we can't logically extrapolate to different conditions. (Hume's truism that induction or generalization is never fully justified logically). External threats include:
Research should be conducted in schools in this manner--ideas for research should originate with teachers or other school personnel. The designs for this research should be worked out with someone expert at research methodology, and the research itself carried out by those who came up with the research idea. Results should be analyzed by the expert, and then the final interpretation delivered by an intermediary. Tests of significance for this design--although this design may be developed and conducted appropriately, statistical tests of significance are not always used appropriately.
The Soloman Four-Group DesignThe design is as:
In this design, subjects are randomly assigned to four different groups: experimental with both pre-posttests, experimental with no pretest, control with pre-posttests, and control without pretests. By using experimental and control groups with and without pretests, both the main effects of testing and the interaction of testing and the treatment are controlled. Therefore generalizability increases and the effect of X is replicated in four different ways. Statistical tests for this design--a good way to test the results is to rule out the pretest as a "treatment" and treat the posttest scores with a 2X2 analysis of variance design-pretested against unpretested. The Posttest-Only Control Group DesignThis design is as: This design can be though of as the last two groups in the Solomon 4-group design. And can be seen as controlling for testing as main effect and interaction, but unlike this design, it doesn't measure them. But the measurement of these effects isn't necessary to the central question of whether of not X did have an effect. This design is appropriate for times when pretests are not acceptable.Statistical tests for this design--the most simple form would be the t-test. However covariance analysis and blocking on subject variables (prior grades, test scores, etc.) can be used which increase the power of the significance test similarly to what is provided by a pretest. As illustrated above, Cook and Campbell devoted much efforts to avoid/reduce the threats against internal valdity (cause and effect) and external validity (generalization). However, some widespread concepts may also contribute other types of threats against internal and external validity. Some researchers downplay the importance of causal inference and assert the worth of understanding. This understanding includes "what," "how," and "why." However, is "why" considered a "cause and effect" relationship? If a question "why X happens" is asked and the answer is "Y happens," does it imply that "Y causes X"? If X and Y are correlated only, it does not address the question "why." Replacing "cause and effect" with "understanding" makes the conclusion confusing and misdirect researchers away from the issue of "internal validity." Some researchers apply a phenomenological approach to "explanation." In this view, an explanation is applied to only a particular case in a particular time and place, and thus generalization is considered inappropriate. In fact, a particular explanation does not explain anything. For example, if one askes, "Why Alex Yu behaves in that way," the asnwer could be "because he is Alex Yu. He is a unqiue human being. He has a particular family background and a specific social circle." These "particular" statements are alway right, thereby misguide researchers away from the issue of external validity. What is a pretesta research design in which the same assessment measures are given to participants both before and after they have received a treatment or been exposed to a condition, with such measures used to determine if there are any changes that could be attributed to the treatment or condition.
What is an example of a pretestPretest-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 effect of a new teaching method upon groups of children.
What is a two group pretestA two-group pretest–posttest design is an experimental design, which compares the change that occurs within two different groups on some dependent variable (the outcome) by measuring that variable at two time periods, before and after introducing/changing an independent variable (the experimental manipulation or ...
What is post test only control group design?The posttest-only control group design is a research design in which there are at least two groups, one of which does not receive a treatment or intervention, and data are collected on the outcome measure after the treatment or intervention.
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