# Psy 625 Week 1

*Time to Practice – Week One*

**Complete** both Part A and Part B below.

** **

## Part A

Some questions in Part A require that you access data from *Statistics for People Who (Think **T**hey) Hate Statistics**. *This data is available on the student website under the Student Test Resources link.

1. By hand, compute the mean, median, and mode for the following set of 40 reading scores:

**SUMMARY**

31 | 32 | 43 | 42 |

24 | 34 | 25 | 44 |

23 | 43 | 24 | 36 |

25 | 41 | 23 | 28 |

14 | 21 | 24 | 17 |

25 | 23 | 44 | 21 |

13 | 26 | 23 | 32 |

12 | 26 | 14 | 42 |

14 | 31 | 52 | 12 |

23 | 42 | 32 | 34 |

2. Compute the means for the following set of scores saved as Ch. 2 Data Set 3 using IBM^{®}SPSS^{®} software. Print out a copy of the output.

Hospital size (number of beds) | Infection rate (per 1,000 admissions) |

234 | 1.7 |

214 | 2.4 |

165 | 3.1 |

436 | 5.6 |

432 | 4.9 |

342 | 5.3 |

276 | 5.6 |

187 | 1.2 |

512 | 3.3 |

553 | 4.1 |

3. You are the manager of a fast food store. Part of your job is to report which special is selling best to the boss at the end of each day. Use your knowledge of descriptive statistics and write one paragraph to let the boss know what happened today. Use the following data. Do not use IBM^{®}SPSS^{®}software to compute the statistics needed; rather, do it by hand. Include a copy of your work.

Special number | Sold | Cost |

Huge Burger | 20 | $2.95 |

Baby Burger | 18 | $1.49 |

Chicken Littles | 25 | $3.50 |

Porker Burger | 19 | $2.95 |

Yummy Burger | 17 | $1.99 |

Coney Dog | 20 | $1.99 |

Total specials sold | 119 |

4. Suppose you are working with a data set that has some different (much larger or much smaller than the rest of the data) scores. What measure of central tendency would you use and why?

5. For the following set of scores, compute the range, the unbiased and the biased standard deviations, and the variance. Do the exercise by hand.

31, 42, 35, 55, 54, 34, 25, 44, 35

Why is the unbiased estimate greater than the biased estimate?

6. Use IBM^{®}SPSS^{®}software to compute all the descriptive statistics for the following set of three test scores over the course of a semester. Which test had the highest average score? Which test had the smallest amount of variability?

Test 1 | Test 2 | Test 3 |

50 | 50 | 49 |

48 | 49 | 47 |

51 | 51 | 51 |

46 | 46 | 55 |

49 | 48 | 55 |

48 | 53 | 45 |

49 | 49 | 47 |

49 | 52 | 45 |

50 | 48 | 46 |

50 | 55 | 53 |

7. This practice problem uses the data contained in the file named Ch. 3 Data Set 3. There are two variables in this data set.

Variable | Definition |

Height | Height in inches |

Weight | Weight in pounds |

Using IBM^{®}SPSS^{®}software, compute all of the measures of variability you can for height and weight.

8. Review the following frequency distribution. Create a histogram either by hand or by using some other application such as a Microsoft^{®}Excel^{®}document.

Class interval | Frequency |

90–100 | 12 |

80–89 | 14 |

70–79 | 20 |

60–69 | 24 |

50–59 | 28 |

40–49 | 29 |

30–39 | 21 |

20–29 | 15 |

10–19 | 17 |

0–9 | 12 |

9. A third-grade teacher is looking to improve her students’ level of engagement during group discussions and instruction. She keeps track of each of the 15 third graders’ number of responses every day for 1 week. This information is available in Ch. 4 Data Set 2. Use IBM^{®}SPSS^{®}software to create a bar chart (one bar for each day).

10. Identify whether these distributions are negatively skewed, positively skewed, or not skewed at all, and why.

a. This talented group of athletes scored very high on the vertical jump task.

b. On this incredibly crummy test, everyone received the same score.

c. On the most difficult spelling test of the year, the third graders wept as the scores were delivered.

11. For each of the following, indicate whether you would use a pie, line, or bar chart, and why.

a. The proportion of freshmen, sophomores, juniors, and seniors in a particular university

b. Change in GPA over four semesters

c. Number of applicants for four different jobs

d. Reaction time to different stimuli

e. Number of scores in each of 10 categories

## From Salkind (2011). Copyright © 2012 SAGE. All Rights Reserved. Adapted with permission.

## Part B

** **

**Complete** the questions below. Be specific and provide examples when relevant.

**Cite** any sources consistent with APA guidelines.

Question | Answer | |

Salkind (2011) describes statistics as a “set of tools” (p. 18). How do behavioral scientists use those tools? | ||

How would you use descriptive statistics to report the effectiveness of a baseball team? How would you use inferential statistics to report the effectiveness of a baseball team? In this example, what is the sample and what is the population? | ||

What does a measure of central tendency tell us about a data set? Identify the three common measures of central tendency used in descriptive statistics and give an example of each. How do you calculate them? | ||

What is variability in a data set? Identify three measures of variability used in descriptive statistics, explain how to calculate each, and give an example of each. | ||