A test of writing ability is given to a random sample of students before and after they completed a formal writing course. The results are given below. Construct a 99% confidence interval for the mean difference between the before and after scores. You may assume the populations are normally distributed.
Before 70 80 92 99 93 97 76 63 68 71 74
After 69 79 90 96 91 95 75 64 62 64 76
Identify each of the following.
a. The justification for normality in this situation.
b. The critical value needed to complete this calculation.
c. The value d-bar (Before – After) that will be used as the point estimate for the calculation of this interval.
d. The value of E, the error found to calculate the interval.
e. The confidence interval for the mean difference between before and after scores.
Before 70 80 92 99 93 97 76 63 68 71 74
After 69 79 90 96 91 95 75 64 62 64 76
Identify each of the following.
a. The justification for normality in this situation.
b. The critical value needed to complete this calculation.
c. The value d-bar (Before – After) that will be used as the point estimate for the calculation of this interval.
d. The value of E, the error found to calculate the interval.
e. The confidence interval for the mean difference between before and after scores.
