Name __________________________________
PSY 512 Experimental Design
Variability Exercise (I-R)
(15 points, #1 1 point/answer; #s 2, 3, & 4 each 1 point)
This assignment is due before the start of class on September 2 and MUST be submitted to steven.haggboom@wku.edu as an email
attachment. Please put 512 (and nothing else) in the subject line of the email.
Problem 1: Let the following scores represent the ages of participants in a psychology experiment concerned with the effects of age on
problem solving. Calculate the mean (
X
) age of participants and the variance (
) and standard deviation (
2) of ages for both groups. Also
calculate the mean number of problems solved, and respective variances and standard deviations, for both groups. You can use a software
program, calculator with a statistic mode, or work through a formula, but use the method for calculating standard deviation and variance that
has n – 1in the denominator.
Group 1: Young Participants
Age (Years) Number of Problems
Solved
17.7 44
18.1 42
19.5 48
22.5 39
18.0 41
18.7 37
19.8 38
23.6 35
21.5 40
21.8 39
24.0 43
25.2 45
X
= _________
X
= ________
s 2 = _________ s2 = ________
s = _________ s = ________
Group 2: Older Participants
Age (Years) Number of Problems Solved
66.2 27
72.1 25
68.7 29
66.5 28
69.7 15
74.8 18
77.4 23
75.5 29
65.5 33
65.8 37
62.0 30
61.4 25
X
= ________
X
= ________
s2 = ________ s2 = ________
s = _________ s = ________
Problem 2: In an experiment such as this, researchers would likely report both the mean age of participants in both groups, and the standard
deviations. Why?
Problem 3: For which group is the mean age of the participants more representative of the age of participants? How do we know that?
Problem 4: There are two methods for calculating variance (and thus also two methods for calculating standard deviation). The only
difference between the two methods is the denominator, either n or n - 1. What determines which method should be used?
