A study was conducted to measure the effectiveness of hypnotism in reducing pain. The measurements are centimeters on a pain scale before and after hypnosis. Assume that the paired sample data are simple random samples and that the differences have a distribution that is approximately normal. Construct a $95 \%$ confidence interval for the mean of the "before - after" differences. Does hypnotism appear to be effective in reducing pain?
Before
8.8
4.1
8.4
11.7
5.9
5.9
1.5
2.4
7.2
8.3
6.4
3.6
2.9
Construct a $95 \%$ confidence interval for the mean of the "before - after" differences.
$< \mu_{d}< $
(Round to two decimal places as needed.)

Step 1 ：A study was conducted to measure the effectiveness of hypnotism in reducing pain. The measurements are centimeters on a pain scale before and after hypnosis. Assume that the paired sample data are simple random samples and that the differences have a distribution that is approximately normal. Construct a $95 \%$ confidence interval for the mean of the 'before - after' differences. Does hypnotism appear to be effective in reducing pain?

Step 2 ：Without the 'after' measurements, we can't calculate the differences or proceed with constructing the confidence interval. Therefore, we can't answer the question.

Step 3 ：\(\boxed{\text{Without the 'after' measurements, we can't calculate the differences or proceed with constructing the confidence interval. Therefore, we can't answer the question.}}\)