18. A researcher would like to determine how physical endurance is affected by a common herbal supplement.

The researcher measures endurance for a sample of n 9 participants. Each individual is then given a 30-day supply of the herbs and, 1 month later, endurance is measured again. For this sample, endurance increased by an average of MD 6 points with SS 216.

a. Make a point estimate of the population mean difference in endurance after taking the herbs.

b. Make a 95% confidence interval estimate of the population mean difference.