Advantages and disadvantages in the use of a posttest-only control group design
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1. What are some advantages and disadvantages in the use of a posttest-only control group design versus a pretest/posttest control group design? (Must identify at least one advantage and one disadvantage per design – so four total).
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2. What is a confound and how is it related to internal validity?
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3. What is the relationship between external validity and the college sophomore problem?
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4. On the most recent exam in your biology class, every student earned an A. The professor claims that he must really be a good teacher for all of the students to have done so well. Given the confounds discussed this week, what alternative explanation can you offer for this result? (Don’t just list a concern– briefly provide a justification).
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5. A health magazine recently reported a study in which researchers claimed that women who take iron supplements have better problem-solving abilities. Further investigation revealed that they assessed problem-solving abilities in a group of women and then had the women self-report whether or not they take iron supplements. Discuss one potential threat to internal validity as it relates specifically to this study.
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Scenario: According to some research, males have better spatial skills than do females; and according to other research, females have better reading skills than males. A student is interested in determining which gender performs better on a word-search puzzle (a puzzle in which words are hidden vertically, horizontally, and diagonally within an array of letters) since this type of puzzle involves both spatial and reading skills. A sample of males and females volunteer to participate and are given 10 minutes to work on a 50-word puzzle. The number of words correctly recognized is recorded for each subject. Use this scenario to answer the following questions.
6)What is the independent variable? Dependent variable? What is the scale of measurement for each? ANSWER
Sample Solution
Post-test only design follows all the same steps as the classic pre-test/post-test design except that it omits the pre-test. There are many situations where a pre-test is impossible because the participants have already been exposed to the treatment, or it would be too expensive or too time-consuming. For large enough groups, this design can control for most of the same threats to internal and external validity as the classic controlled experimental design. For example, it eliminates the threat to internal validity of pre-testing by eliminating the pre-test. A disadvantage of only having a posttest design is you are less aware of the likelihood for participants to drop out during the study.
