1. Explain what counterbalancing is, how it is achieved, and which confound it helps to minimize.
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2. Using your own words, discuss how a correlated-groups t test has more statistical power in comparison to an independent-groups t test.
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3. Discuss one strength and one weakness of a within-subjects design using your own words. (Do not include statistical power, as it is assessed in a previous question)
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SCENARIO: A researcher believes exercise may affect anxiety in women, but research appears inconclusive. She identifies a group of women (N = 30) who had not exercised before, but are now planning to begin exercising. She gives them a 50-item anxiety inventory before they begin exercising and administers it again after 6 months of exercising. The anxiety inventory is measured on an interval scale and higher numbers indicate higher anxiety. In addition, scores on the inventory are normally distributed. The mean of the difference scores is 3.4, SD = 1.8, and there were 30 in the sample. Using this information, answer the following questions showing all work when calculations are required to earn up to full credit.
4) Calculate the correlated-groups t test to determine the tobt. (Note you will first have to solve for the standard error of the difference score).
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5) Calculate the effect size using Cohen’s d. Interpret it using the appropriate conventions (small, medium, or large).
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6) Is this a directional or non-directional study, and what is the t cv? (Note you will have to first calculate the df)
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7) Calculate the 95% confidence intervals (make sure you use the two-tailed t cv ).
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8) Write an APA-style Results section based on your analyses. All homework “Results sections” should follow the examples provided in the videos. Don’t forget to include the effect size, confidence interval, and a decision about the null hypothesis.
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