stat homework

Research Methods in Psychology

Assignment 7

1. An experimenter was interested in the effects of diet and exercise on weight loss. In particular, she was interested in whether exercise would provide any benefits compared to no exercise in the absence of an accompanying diet. Subjects were randomly assigned to one of four conditions that factorially combined diet/no diet and exercise/no exercise. Results of the experiment indicated that subjects not on a diet lost only two pounds (on average) whether or not they exercised. However, subjects who dieted lost ten pounds (on average) if they exercised and six pounds (on average) if they dieted without exercising.

a) Diagram (using a box diagram/matrix) the experimental design, and fill in the numerical results. Be sure to include all cell and marginal means; assume equal n (i.e., # subjects) in each cell. Then graph the results; be sure to properly label the parts of your graph. 5 pts

b) Interpret the results in words, i.e., in terms of main and interaction effects. Note: There are 3 effects you need to discuss. Be sure to cite the specific numbers you would use to back up each of your three interpretive statements. Assume (1) equal n in each cell and (2) that any difference between means is significant. Finally, answer the experimenter’s original question: “Does exercise provide any benefits compared to no exercise in the absence of an accompanying diet?” Note: The experimenter is asking about the presence of something called a simple effect (your book refers to it as a simple main effect). 5 pts.

2. Suppose an experimental investigation was undertaken in which 15 patients with hypertension were treated with an antihypertensive drug. Diastolic blood pressure (in mm Hg) was carefully measured under resting conditions before therapy (pretreatment), and then after six weeks of therapy (treatment). The data are presented below.

Patient Pretreatment Treatment

1 106 96

2 105 92

3 96 90

4 113 91

5 112 114

6 122 103

7 98 81

8 101 105

9 115 95

10 107 89

11 99 102

12 109 84

13 112 91

14 104 88

15 100 85

a) Conduct a paired t-test on the data using SPSS. You should read Chapter 7 of “A Crash Course in SPSS,” if you need help. Was the treatment effective in reducing hypertension (i.e., blood pressure)? Properly report the results of the t-test to support your answer. Be sure to print out and turn in a copy of your summary results. 3 pts

b) Conduct a Wilcoxon Matched-Pairs Test on the same set of data. You may want to read Chapter 8 of a “Crash Course in SPSS.” Was the treatment effective? How does the level of significance here compare to that found in (a)? Why does the significance level differ? Be sure to print out and turn in a copy of your SPSS summary results. 3 pts

Read Chapter 8 from Seeing Statistics. Then answer the question below.

3. Answer Question 4 (about the dam) in Chapter 8.8 (Exercises for Inference & Confidence). 4 pts