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.