# PSYCH 625 Week 2 Individual Assignment Time to Practice Parts (A,B,C)

Time to Practice – Week Two

Complete Parts A, B, and C below.

Part A

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

1. Why is a z score a standard score? Why can standard scores be used to compare scores from different distributions?

2. For the following set of scores, fill in the cells. The mean is 70 and the standard deviation is 8.

Raw score

Z score

68.0

?

?

–1.6

82.0

?

?

1.8

69.0

?

?

–0.5

85.0

?

?

1.7

72.0

?

3. Questions 3a through 3d are based on a distribution of scores with and the standard Draw a small picture to help you see what is required.

a. What is the probability of a score falling between a raw score of 70 and 80?

b. What is the probability of a score falling above a raw score of 80?

c. What is the probability of a score falling between a raw score of 81 and 83?

d. What is the probability of a score falling below a raw score of 63?

4. Jake needs to score in the top 10% in order to earn a physical fitness certificate. The class mean is 78 and the standard deviation is 5.5. What raw score does he need?

5. Who is the better student, relative to his or her classmates? Use the following table for information.

Math

Class mean

81

Class standard deviation

2

Reading

Class mean

87

Class standard deviation

10

Raw scores

Math score

Reading score

Average

Noah

85

88

86.5

Talya

87

81

84

Z-scores

Math score

Reading score

Average

Noah

Talya

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

Part C

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

Cite any sources consistent with APA guidelines.

Question

Answer

What is the relationship between reliability and validity? How can a test be reliable but not valid? Can a test be valid but not reliable? Why or why not?

How does understanding probability help you understand statistics?

How could you use standard scores and the standard distribution to compare the reading scores of two students receiving special reading resource help and one student in a standard classroom who does not get special help?

In a standard normal distribution: What does a zscore of 1 represent? What percent of cases fall between the mean and one standard deviation above the mean? What percent fall between the mean and –1 to +1 standard deviations from the mean? What percent of scores will fall between –3 and +3 standard deviations under the normal curve?