One-Way Repeated-Measures ANOVA Continued
QUESTION 2: WHAT’S THE STRENGTH OF THE RELATIONSHIP?
- Since we are able to separate out the variability due to individual differences (SSacross subjects), we can compute our eta-squared more precisely by using SSiv + SSerror in the denominator rather than SStotal
- This tells us that 44% of the variability in the DV (perceived influence on children) is associated with the IV (type of media – television v. movies v. rock music) – a strong effect
- It’s important to keep in mind that this is the proportion of variability in the DV after the effects of individual differences have been removed.
- (This was also true of the correlated-groups t-test)
QUESTION 3: WHAT’S THE NATURE OF THE RELATIONSHIP?
- We found a statistically significant effect of media type on perceived influence on children – what’s the nature of the effect?
- Which types of media are seen as more positive or negative than the others?
- Again, we’ll need to make a comparison of each group 
to each of the other group s – we use the Tukey HSD procedure again:
|
Comparison |
Absolute Difference |
||
|
|
|2.00 – 3.75| = 1.75 |
||
|
|
|2.00 – 2.25| = .25 |
||
|
|
|3.75 – 2.25| = 1.50 |
- We determine our "critical difference" (CD), using:
- We already know MSerror and N – we get q (Studentized range value) from Appendix G (p. 592):
- So, 
- Now we just compare our absolute difference to the critical difference – if higher, reject null, if lower, do not reject null for that comparison
|
Comparison |
Absolute Difference |
CD |
Statistically Significant? |
|
|
|2.00 – 3.75| = 1.75 |
1.497 |
Yes |
|
|
|2.00 – 2.25| = .25 |
1.497 |
No |
|
|
|3.75 – 2.25| = 1.50 |
1.497 |
Yes |
- Go back to original group means to express significant differences in words.
- Our Tukey procedure shows that on average, people perceive both Television (M = 2.00) and Rock Music (M = 2.25) to have statistically significantly more negative influence on children than do Movies (M = 3.75)
- Or you could say that movies were rated statistically significantly more positively than TV or Rock Music.
