Homework 7

Confidence Intervals, Effect Size, and Statistical Power

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Confidence Intervals, Effect Size, and Statistical Power

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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 text-based questions or the APA Participants section) in the appropriate place within the same file.

Part I: Questions 2-5

End-of-chapter 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 two-tailed test.

4a) 80% (Hint: 10% in each tail): Answer

Work:

4b) 88% Answer

Work:

5)

Remembering that a meta-analysis calculates one mean effect size using the effect sizes of several studies, assume you are conducting a meta-analysis 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 6-8

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.

Compute the effect size of the new sales program.

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.

What is the effect size of the relaxation program?

Answer

Work:

8)

A residential treatment facility tests a new group therapy for patients with self-destructive behaviors. The therapists hope to decrease scores on a measure of self-destructive 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.

What is the effect size of the new group therapy?

Answer

Work:

Helping Behaviors

47

52

40

39

50

32

47

65

43

59

56

39

63

45

46

54

35

61

56

52

Part IV:

Questions 1-4

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.

1-a)

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 45th 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 5a-5e

For the following scores, state the: a) mean; b) median; c) mode; d) range; e) standard deviation.

39 35 43 27 35

5-a)

Mean

Answer

Work:

5-b)

Median

Answer

Work:

5-c)

Mode

Answer

Work:

5-d)

Range

Answer

Work:

5-e)

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.

Done!

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