Exam 8: Confidence Interval Estimation

TABLE 8-10 The president of a university would like to estimate the proportion of the student population that owns a personal computer. In a sample of 500 students, 417 own a personal computer. -Referring to Table 8-10, the critical value for a 99% confidence interval for this sample is______

TABLE 8-3 A quality control engineer is interested in the mean length of sheet insulation being cut automatically by machine. The desired length of the insulation is 12 feet. It is known that the standard deviation in the cutting length is 0.15 feet. A sample of 70 cut sheets yields a mean length of 12.14 feet. This sample will be used to obtain a 99% confidence interval for the mean length cut by machine. -Referring to Table 8-3, suppose the engineer had decided to estimate the mean length to within 0.03 with 99% confidence. Then the sample size would be _____.

A population parameter is used to estimate a confidence interval.

TABLE 8-2 The managers of a company are worried about the morale of their employees. In order to determine if a problem in this area exists, they decide to evaluate the attitudes of their employees with a standardized test. They select the Fortunato test of job satisfaction, which has a known standard deviation of 24 points. -Referring to Table 8-2, this confidence interval is only valid if the scores on the Fortunato test are normally distributed.

Suppose a 95% confidence interval for µ has been constructed. If it is decided to take a larger sample and to decrease the confidence level of the interval, then the resulting interval width would be ____. (Assume that the sample statistics gathered would not change very much for the new sample.)