A researcher would like to evaluate the effectiveness of a pain-relief patch designed for lower back pain. Prior to testing the patch, each of n = 8 patients rates the current level of back pain on a scale from 1 to 10. After wearing the patch for 90 minutes, a second pain rating is recorded. The data are as follows:
| |
Before
|
After
|
| |
6
|
2
|
| |
8
|
3
|
| |
9
|
4
|
| |
8
|
1
|
| |
10
|
2
|
| |
5
|
3
|
| |
9
|
8
|
| |
7
|
7
|
|
|
|
|
|
a. Compute the mean and variance for the sample of difference scores.
b. Do the results indicate a significant difference? Use a two-tailed test with a= .05
c. Compute Cohen's d to measure the size of the effect.