Homework 7
Confidence Intervals, Effect Size, and Statistical Power
Complete all analyses in SPSS, then copy and paste your output and graphs into your homework document file. Answer any written questions (such as the textbased questions or the APA Participants section) in the appropriate place within the same file.
 Part I: Questions 25 Endofchapter problems: Complete the following problems.
If applicable, remember to show work in your homework document to receive partial credit.
 
4)  For each of the following confidence levels, look up the critical z values for a twotailed test.  
4a) 80% (Hint: 10% in each tail): Answer  Work:  
4b) 88% Answer  Work:  
5)  Remembering that a metaanalysis calculates one mean effect size using the effect sizes of several studies, assume you are conducting a metaanalysis over a set of five studies. The effect sizes for each study are: d= .80, d = .09, d = .46, d = .65, d = .28  
5a) Calculate the mean effect size of these studies. Answer 
 
5b) Use Cohen’s conventions to describe the mean effect size you calculated in part (a). Answer  
 
 Part I: Questions 68
Compute effect size in the following questions:  
6)  A company decides to add a new program that prepares randomly selected sales personnel to increase their number of sales per month. The mean number of sales per month for the overall population of sales personnel at this national company is 25 with a standard deviation of 3. The mean number of sales per month for those who participated in the new program is 30.  
Answer  Work:  
7)  On a certain anxiety questionnaire, the general population is known to have a mean of 16 and a standard deviation of 2.4. A higher score represents higher levels of anxiety. Participants in a new relaxation program complete the questionnaire after completing the program and have a mean score of 12.5.  
Answer  Work:  
8)  A residential treatment facility tests a new group therapy for patients with selfdestructive behaviors. The therapists hope to decrease scores on a measure of selfdestructive behaviors that has a mean in the overall residential treatment population of 15 and a standard deviation of 1.6. The mean score for the patients after the new group therapy is 13.7.  
Answer  Work:  

Part IV: A test designed to measure helping behavior was administered to 20 university students. The data from this test are shown in the column to the left. (higher scores à more helping). · Enter the Helping Behaviors data into a new SPSS file.  
 
1a)  Using SPSS, calculate descriptive statistics for this variable. Be sure to include the mean and standard deviation.
 
Answer: Descriptive Statistics Table
 
2)  Create the appropriate graph in SPSS for the variable “Helping Behaviors.” Justify your choice of graph.  
Answer: Appropriate graph
 
Justification  
3)  Using the mean and standard deviation of the helping behaviors data above (from your SPSS output), calculate (by hand) the raw score that marks the 45^{th} percentile of this data set. (See last week’s material for review.)  
Answer  Work:
 
4)  Using the mean and standard deviation of the helping behaviors data above, calculate the percentile of a raw score of 37. (See last week’s material for review.)  
Answer  Work:
 
 Part IV: Question 5a5e For the following scores, state the: a) mean; b) median; c) mode; d) range; e) standard deviation.
 
5a)  Mean  
Answer  Work:  
5b)  Median  
Answer  Work:  
5c)  Mode  
Answer  Work:  
5d)  Range  
Answer  Work:  
5e)  Standard Deviation (Note: Compute by hand using the formula from Module 3. Programs like SPSS or Excel use a slightly different formula that we won’t use until Module 8 and will give you the wrong answer for this section.)  
Answer  Work:  
Submit Homework 7 by 11:59 p.m. (ET) on Monday of Module/Week 7. Remember to name file appropriately.
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