Correlated-Two-Groups Design

Part I: General Concepts

Answer the following questions using your own words.

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).

Work:

ANSWER t obtained:

5) Calculate the effect size using Cohen’s d. Interpret it using the appropriate conventions (small, medium, or large).

Work:

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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)

Work:

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7) Calculate the 95% confidence intervals (make sure you use the two-tailed t cv ).

Work:

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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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Part II: SPSS Application

Research Scenario: Do you cope better than peers when facing difficult situations? In one study, researchers reported that most individuals believe that they can cope better than their fellow students (Igou, 2008). A recent researcher wanted to replicate the study. In this design, participants read a scenario of a negative event and were asked to use a 10 point scale to rate how it would affect their immediate well being (1 – 10, the higher the score, the better the mood). They they were asked to imagine the event from the perspective of an ordinary fellow student and rate how it would affect that person using the same scale.

Using the information provided, create an SPSS data file and conduct the appropriate statistical test to determine whether people believe they can cope better than their peers. Answer the following questions based on your analyses.

9) Conduct a correlated groups t-test. Paste the appropriate SPSS output below.

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10) Use the output to calculate r2 (show your work in the space provided and remember if a number is negative, when squaring it will lose its sign and be positive). Interpret it (small, medium, large) based on the conventions for this effect size calculation.

Work:

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11) Paste an appropriate SPSS graph (make sure you use the procedures outlined in this module’s SPSS video– and don’t forget to label your y axis “Coping Ability”.

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12) 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. If significant, make sure you interpret how the conditions differ (refer to the Figure or report the means and standard deviations).

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Part III: Cumulative

Does amount of information retained differ when participating in meetings in-person verses virtually? In this study, participants got to choose whether they attend a quarterly meeting in person or via Google Meet. After the meeting, they were given a brief assessment of information covered – percent correct for each condition is presented in the table below.

Using the information provided, create an SPSS data file and conduct the appropriate statistical test to determine whether there is a statistically significant difference in amount of information retained based on whether attendance is in-person or virtual. Answer the following questions based on your analysis.

13)

Clearly identify the independent and dependent variables in this scenario.

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14)

Paste the output of your statistical analysis below.

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15)

Create an appropriate graph based on the data and paste it below (make sure to have axes labels and error bars).

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16)

Write an APA-style Results section based on your analyses. Remember to use complete sentences, include the statistical notation, effect size, confidence interval, and include a decision about the null hypothesis. If it is significant, state how by reporting the means and standard deviations or refer the reader to the previous Figure.

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17)

Discuss one threat to internal validity as it specifically relates to this research scenario.

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Use this information to answer the following questions:

· Age at onset of dementia was determined in the general population to be  = 70 and  = 7.0.

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