54 Orthodontics and one-way between-groups ANOVA:Iranian researchers studied factors affecting patients' likelihood of wearing orthodontic appliances, noting that orthodontics is perhaps the area of health care with the highest need for patient cooperation (Behenam & Pooya, 2007). Among their analyses, they compared students in primary school, junior high school, and high school. The data that follow have almost exactly the same means as the researchers found in their study, but with far smaller samples. The score for each student is his or her daily hours of wearing the orthodontic appliance.

• Primary school: 16, 13, 18
• Junior high school: 8, 13, 14, 12
• High school: 20, 15, 16, 18

1. What is the independent variable? What are its levels?
2. What is the dependent variable?
3. Conduct all six steps of hypothesis testing for a one-way between-groups ANOVA.
4. How would you report the statistics in a journal article?
5. Conduct a TukeyHSDtest. What did you learn?
6. Calculate the traditional effect size for this sample.
7. Calculate the more conservative estimate of effect size for this sample. How does this estimate differ from the one you calculated in part (f)?
8. Based on Cohen's conventions, are these small, medium, or large effect sizes?
9. Why is it useful to know the effect size in addition to the results of a hypothesis test?
10. How could this study be conducted using a within-groups design?