1. In a study of the effects of stress on illness, a researcher tallied the number of colds people contracted during a 6-month period as a function of the amount of stress they reported during that same time period. There were three stress levels: minimal, moderate, and high stress. The sums of squares appear in the following ANOVA summary table. The mean for each condition and the number of subjects per condition are also noted.
Source df SS MS F
Between groups 22.167
Within groups 14.750
Total 36.917
Stress Level Mean N
Minimal 3 4
Moderate 4 4
High 6 4
a. Complete the ANOVA summary table.
b. Is Fobt significant at a = .05; at a = .01?
c. Perform post hoc comparisons if necessary.
d. What conclusions can be drawn from the F-ratio and the post hoc comparisons?
e. What is the effect size, and what does this mean?
f. Graph the means.
2. A researcher conducted an experiment on the effects of a new "drug" on depression. The researcher had a control group that received nothing, a placebo group, and an experimental group that received the "drug." A depression inventory that provided a measure of depression on a 50-point scale was used (50 indicates that an individual is very high on the depression variable). The ANOVA summary table appears next, along with the mean depression score for each condition.
Source df SS MS F
Between groups 1,202.313
Within groups 2,118.00
Total 3,320.313
"Drug" Condition Mean n
Control 36.26 15
Placebo 33.33 15
"Drug" 24.13 15
a. Complete the ANOVA summary table.
b. Is Fobt significant at a = .05; at a = .01?
c. Perform post hoc comparisons if necessary.
d. What conclusions can be drawn from the F-ratio and the post hoc comparisons?
e. What is the effect size, and what does this mean?
f. Graph the means.
3. A researcher has been hired by a pizzeria to determine which type of crust customers prefer.
The restaurant offers three types of crust: hand-tossed, thick, and thin. Following are the mean number of 1-inch pieces of pizza eaten for each condition from 10 subjects who had the opportunity to eat as many pieces with each type of crust as they desired. The ANOVA summary table also follows.
Source df SS MS F
Subject 2.75
Between 180.05
Error 21.65
Total 204.45
Crust Type Mean n
Hand-tossed 2.73 10
Thick 4.20 10
Thin 8.50 10
a. Complete the ANOVA summary table.
b. Is Fobt significant at a = .05; at a = .01?
c. Perform post hoc comparisons if necessary.
d. What conclusions can be drawn from the F-ratio and the post hoc comparisons?
e. What is the effect size, and what does this mean?
f. Graph the means.