A study was conducted to investigate the effectiveness of hypnotism in reducing pain. Results for randomly selected subjects are given in the accompanying table. The values are before and after hypnosis; the measurements are in centimeters on a pain scale. Construct a 95% confidence interval for the mean of the €œbefore/after€ differences. Does hypnotism appear to be effective in reducing pain?

Assume that the paired sample data are simple random samples and that the differences have a distribution that is approximately normal.

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Subject Before After 6.6 6.59.0 10.3 11.3 8.1 6.3 11.6 6.8 2.4 7.4 8.5 8.1 6.1 3.4 2.0