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# PS390 Statistical Reasoning in Psychology

**ASSIGNMENT 04**

PS390 Statistical Reasoning in Psychology

**Directions: **Be sure to save an electronic copy of your answer before submitting it to Ashworth College for grading. Unless otherwise stated, answer in complete sentences, and be sure to use correct English, spelling, and grammar. Sources must be cited in APA format. Your response should be four (4) double‐spaced pages; refer to the “Format Requirementsʺ page for specific format requirements.

**StatCrunch**

StatCrunch tutorial videos are available at http://www.youtube.com/view_play_list?p=BE055F65E43B4973.

1. (25 points) A prison psychologist recorded the number of rule infractions for 15 prison inmates over a six-month period to be 5, 4, 2, 4, 3, 5, 2, 0, 4, 4, 5, 5, 3, 4, and 3.

a. Make a frequency table.

b. Make a histogram based on the frequency table.

c. Describe in words the shape of the histogram.

2. (25 points) Identify and solve this problem by hand.

The head of public safety notices that the average driving speed at a particular intersection averages μ = 35 mph with a standard deviation of σ = 7.5 mph. After a school speed limit sign of 20 mph is placed at the intersection, the first 40 cars travel past at an average speed of 32 mph. Using the .01 significance level, was there a significant change in driving speed?

a. Use the five steps of hypothesis testing (report results in APA format).

b. Sketch the distributions involved.

c. Figure the confidence limits for the 99% confidence interval.

3. (25 points) You will have to use a combination of StatCrunch and hand calculations (e.g., effect sizes) to solve the following problems.

A social psychologist gave a questionnaire about concern for farm workers to seven participants before and after they attended a film about union organization of farm workers. The results are shown below with high scores meaning high concern. Using the .05 significance level, do these results support the hypothesis that the film affected concern for the lives of farm workers?

**Scores on the Concern Measure**

Participant Before After

A 17 20

B 7 4

C 10 11

D 13 15

E 8 5

F 9 8

G 11 14

a. Use the five steps of hypothesis testing.

b. Figure the effect size and find the approximate power of this study.

c. Report results in APA format.

4. (25 points) You will have to use a combination of StatCrunch and hand calculations (e.g., effect sizes) to solve the following problems.

A team of cognitive psychologists studying the effects of sleep deprivation on short-term memory decay had eight participants stay in a sleep lab for two days. Four participants were randomly assigned to a condition in which they were not permitted to sleep during that period, while the other four participants were allowed to sleep when they wanted to. At the end of the two days, the participants completed a short-term memory task that yielded the results in the table that follows. Using the .05 significance level, did sleep deprivation reduce short-term memory?

**Mean Number of Letters Remembered**

Sleep Deprived Normal Sleep

7 9

8 8

7 11

9 7

a. Create the appropriate graph for this problem.

b. Use the five steps of hypothesis testing.

c. Figure the effect size.

d. Report results in APA format.