Question

What statistical tool should I use in a pretest posttest control group design?

Answer 1

what is pretest post test design:

pretest and post test design is a concept in design of experiments,The main requirement of this concept is we can able to check the effect of a variable before usage and after usage on a group.

For example:

In this design, which uses two groups, one group is given the treatment and the results are gathered at the end. The control group receives no treatment, over the same period of time, but undergoes exactly the same tests.

Statistical analysis can then determine if the intervention had a significant effect. One common example of this is in medicine; one 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, can be slightly more complex. For example, if different dosages of a medicine are tested, the design can be based around multiple groups.

However, the most usual method is to randomly assign the participants to groups in order to control for confounding variables. Three main types of pretest post design are commonly used:

1. Randomized Control-Group Pretest Posttest Design.
2. Randomized Solomon Four-Group Design.
3. Nonrandomized Control Group Pretest-Posttest Design.

1. Randomized Control-Group Pretest Posttest Design.:

  The pre-test post-test control group design is also called the classic controlled experimental design. The design includes both a control and a treatment group. For example, if you wanted to gauge if a new way of teaching math was effective, you could:

• Randomly assign participants to a treatment group or a control group.
• Administer a pre-test to the treatment group and the control group.
• Use the new teaching method on the treatment group and the standard method on the control group, ensuring that the method of treatment is the only condition that is different.
• Administer a post-test to both groups.
• Assess the differences between groups.

Two issues can affect the Randomized Control-Group Pretest Posttest Design:

• Internal validity issues: maturation (i.e. biological changes in participants can affect differences between pre- and post-tests) and history (where participants experience something outside of the treatment that can affect scores).
• External validity issues: Interaction of the pre-test and the treatment can occur if participants are influenced by the tone or content of the question. For example, a question about how many hours a student spends on homework might prompt the student to spend more time on homework.

2. Randomized Solomon Four-Group Design:

  In this type of pretest posttest design, four groups are randomly assigned: two experimental groups E1/E2 and two control groups C1/C2. Groups E1 and C1 complete a pre-test and all four groups complete a post-test. This better controls for the interaction of pretesting and posttesting; in the “classic” design, participants may be unduly influenced by the questions on the pretest.

3. Non randomized Control Group Pretest Posttest Design.

This type of test is similar to the “classic” design, but participants are not randomly assigned to groups. Non randomization can be more practical in real-life, when you are dealing with groups like students or employees who are already in classes or departments; randomization (i.e. moving people around to form new groups) could prove disruptive. This type of experimental design suffers from problems with internal validity more so than the other two types.

we can analyse the pretest and post test by means of an ANOVA on change score's,or,what amounts to the same thing,a repeated measures ANOVA to test the treatment by occasion interaction.Although the analysis of acange scores has intuitive appeal such analyses are often inappropriate.An ANCOVA on posttest scores with pretest scores as co-variate usually provides a more appropriate and informative analysis.