Activity 5: T Test and ANOVA (10 Points) Conducting Tests In Activity #4 you learned how to examine relationships between variables, conduct analyses related to correlation and regression, and interpret the output associated with each. In this activity, you will learn how to conduct tests that determine if there are differences between mean scores for groups. For example, you might be interested in studying whether there are mean differences in heart rate between two groups: those who exercise and those who do not (t-test), or you might need a slightly more complicated design to compare mean heart rates for three groups: non-exercisers, occasional exercisers, and regularly exercisers (ANOVA). To Prepare for Activity #5: Read Chapters 9 and 10 in the text. It will be to your advantage to have SAS open on your computer as you work through chapters 9 and 10. While you are reading through this chapter and testing the assumptions of various statistical procedures, consider various types of datasets and whether they would run the risk of violating these assumptions. Also, be sure to download and review the Assignment 5 Tutorial file in the Additional Resources section. Complete Smart Alexs Quizzes. Be sure to take Smart Alexs Quiz at the end of the Chapter and spend time learning the concepts related to questions you answered incorrectly. Answers are available at: http://www.sagepub.com/field3e/SmartAlexAnswers.htm Activity #5 You will submit one Word document and one SAS data file for this activity. You will create the Word document by cutting and pasting SAS output into Word. Please read the instructions below to ensure you are pasting the correct material into your activity document. The Word document will be named LastnamefirstinitialSTAT8028-5a and the SAS document as -5b. Part A. Dependent T-Test In this activity, you are interested in finding out whether participation in a creative writing course results in increased scores of a creativity assessment. For this part of the activity, you will be using the data file Activity5a.sas7bda. In this file, Participant is the numeric student identifier, CreativityPre contains creativity pre-test scores, and CreativityPost contains creativity post-test scores. A total of 40 students completed the pre-test, took the creative writing course, and then took the post-test. 1. Exploratory Data Analysis/Hypotheses. a. Perform exploratory data analysis on CreativityPre and CreativityPost. Using SAS, calculate the mean and standard deviation of these two variables. b. Construct an appropriate chart/graph that displays the relevant information for these two variables. c. Write the null and alternative hypotheses used to test the question above (e.g., whether participation in the course affects writing scores). 2. Comparison of Means a. Perform a dependent t-test to assess your hypotheses above (note that many versions of SAS use the term paired samples t-test rather than dependent t-test; the test itself is the same. b. Write one or two paragraphs that describe the dataset, gives your hypothesis, and presents the results of the dependent sample t-test. Be sure that your writing conforms to APA style. Part B. Independent t-test In this activity, you will start with the data file used in Part A (Activity5a.sas7bda). Suppose, however, you [the researcher] encountered a small problem during data collection: after the post-tests were collected, you realized that the post-test form did not ask for the students identification number. As such, it will be impossible to match pre-test scores to post-test scores. Rather than simply give up, you start thinking about the data you do have, and try to determine whether you can salvage your project. In assessing the situation, you realize that you have 40 pre-test scores and 40 post-test scores, but no way to link them. While it will result in a weaker comparison, you determine that you are still able to compare pre-test vs. post-test scores; you will use a between-subjects design rather than a within-subjects design. 1. Create the data set. a. Using the Activity5a.sas7bda file as a starting point, create a new dataset that you can use with the between subjects design. Hint: you will no longer need the variables CreativePre and CreativeTest. Instead, you have only one variable for the score on the creativity test. A second (or grouping) variable will serve to indicate which test the student took. b. Submit the dataset as Activity5b.sas7bda files. 2. Exploratory Data Analysis/Hypotheses. a. Perform exploratory data analysis on CreativityPre and CreativityPost. Using SAS, calculate the mean and standard deviation of these two variables. b. Construct an appropriate chart/graph that displays the relevant information for these two variables. c. Write the null and alternative hypotheses used to test the question above (e.g., whether participation in the course affects writing scores). 3. Comparison of Means a. Perform an independent t-test to assess your hypotheses above (note that many versions of SAS use the term independent samples t-test rather than simply independent t-test). b. Write one or two paragraphs that describe the dataset, gives your hypothesis, and presents the results of the independent sample t-test. Be sure that your writing conforms to APA style. 4. Comparison of Designs a. In this activity you used the same dataset to analyze both a between- and within-subjects design. Create a single paragraph (using the material you wrote above), that presents both sets of results. b. Explain, in one to two pages (app. 300-500 words), whether the two tests resulted in the same findings. Did you expect this to be the case? Why or why not? What have you learned in this activity? Part C. ANOVA All of us have had our blood pressure measured while at our physicians office. How accurate are these measurements? It may surprise you to learn that there is something called White coat syndromethe tendency of some people to exhibit elevated blood pressure in clinical (medical) settings only. In other words, for these people the very fact that the physician is taking their blood pressure causes it to increase (for more information about white coat syndrome see http://www.webmd.com/anxiety-panic/features/beyond-white-coat-syndrome). In this activity, you will be using the Activity5c.sas7bda data file to determine whether you find support for the existence of white coat syndrome. In this study, 60 participants were randomly assigned to one of three groups. The settings variable indicates the location in which the participants blood pressure was recorded: 1=home, 2=in a doctors office, and 3=in a classroom setting. The SystolicBP variable contains the participants systolic pressure (the upper number). The DiastolicBP variable contains the participants diastolic pressure (the lower number). 1. Exploratory Data Analysis/Hypotheses. a. Perform an exploratory data analysis on both the SystolicBP and DiastolicBP variables. Using SAS, calculate the mean and standard deviation of these two variables. Be sure that your analysis is broken down by setting (e.g., you will have six means, six SDs, etc.). b. Create two graphsone for systolic and one for diastolic pressure. Each graph should clearly delineate the three groups. c. Write a null and alternative hypothesis for the comparison of the three groups (note that your hypothesis will state that the three groups are equivalent; be sure to word your null hypothesis correctly). 2. ANOVA. a. Using the Activity5c.sas7bda data file, perform two single factor ANOVAs: one using SystolicBP and one using DiastolicBP as the dependent variable. b. If appropriate for either or both of the ANOVAs, perform post hoc analyses to determine which groups actually differ. c. Write one paragraph for each ANOVA (be sure to use APA style). At a bare minimum, each paragraph should contain the three means, three SDs, ANOVA results (F, df), post hoc tests (if applicable), effect size, and an interpretation of these results. Submit your files in the Course Work area below the Activity screen. Learning Outcomes: 2, 3, 4, 5, 9 Develop appropriate null and alternative hypotheses given a research question. Evaluate descriptive statistical analysis and visual displays of data. Apply appropriate statistical tests based on levels of measurement. Calculate the appropriate use of inferential statistical analysis. Demonstrate proficiency in the use of SAS and the reporting of statistical output in APA format.
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