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

Part I: Concepts Questions 18 These questions are based on the Nolan and Heinzen reading and end-of-chapter questions.

	Part I: Questions 1a-1e Fill in the highlighted blanks with the best word or words.
1-a)	The confidence interval is centered around the ________ of the sample.
1-b)	Cohen's d measures the difference between means in terms of ________.
1-c)	According to Cohen's conventions, a d value of ________ indicates a small effect.
1-d)	A study that calculates the mean effect size from the individual effect sizes of many studies is called a(n) ________.
1-e)	Statistical power refers to the probability of successfully rejecting the ________.

	Part I: Questions 2-5 End-of-chapter problems: Complete the following Nolan and Heinzen end-of-chapter exercises for Chapter 8: 8.15, 8.22, 8.26, and 8.40. If applicable, remember to show work in your homework document to receive partial credit.
2)	List five factors that affect statistical power. For each, indicate how a researcher can leverage/manipulate that factor to increase power in a study.
A) B) C) D) E)
3)	Exercise 8.22 from N&H text: In 2006, approximately 47% of Americans, when surveyed by a Gallup poll, felt that having a gun in the home made them safer than having no gun. The margin of error reported was 3%. Construct an interval estimate using these figures.
Answer
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:
4c) 95% 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= .76, d = .05, d = .41, d = .63, d = .20
5a) Calculate the mean effect size of these studies. Answer
5b) Use Cohens conventions to describe the mean effect size you calculated in part (a). Answer

	Part I: Questions 6-8
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 29 with a standard deviation of 3.5. The mean number of sales per month for those who participated in the new program is 31. Compute the effect size of the new sales program.
Answer	Work:
7)	On a certain anxiety questionnaire, the population is known to have a mean of 15 and a standard deviation of 2. 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 12.8 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 1.7. The mean score for the patients after the new group therapy is 13.9. What is the effect size of the new group therapy?
Answer	Work:

Part II & Part III There is no new SPSS material this module/week. No questions for Part II or III .

Part IV: Cumulative Data provided below for respective questions.

Helping Behaviors
45 51 42 42 51 33 47 65 46 58	59 38 64 41 46 54 35 60 57 51

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 more helping).

• Enter the Helping Behaviors data into a new SPSS file.

1-a)

Using SPSS, calculate the appropriate descriptive statistics of central tendency and variability (one of each) for this variable.

Justify why you chose each measure.

Answer: Descriptive Statistics Table

1-b)

Justify why you chose each measure.

Central Tendency: Answer

Justification

Variability:

Answer

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 30^th percentile of this data set. (Treat this as you would any problem calculating percentages under the normal curve).

Answer

Work:

4)

Using the mean and standard deviation of the helping behaviors data above, calculate the percentile of a raw score of 37. (Treat this as you would any problem calculating percentages under the normal curve).

Answer

Work:

	Part IV: Question 5a-5e For the following scores, state the: a) mean; b) median; c) mode; d) range; e) standard deviation. 68 54 57 61 59
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 wont use until Module 8 and will give you the wrong answer for this section.)
Answer	Work: