A researcher hypothesizes that people who listen to classical music have higher concentration skills than those in the general population. On a standard concentration test, the overall mean is 15.5. The researcher gave this same test to a random sample of 12 individuals who regularly listen to classical music. Their scores on the test were as follows:

16, 14, 20, 12, 25, 22, 23, 19, 17, 17, 21, 20

1. Is this a one- or two-tailed test?
2. Conduct all 6 steps of the appropriate statistic. Be sure to label all six steps.
3. Calculate and interpret the effect size for this test.