Exam 12: Comparing Two Means

A consumer group was interested in comparing the operating time of cordless toothbrushes manufactured by two different companies. Group members took a random Sample of 18 toothbrushes from Company A and 15 from Company B. Each was charged Overnight and the number of hours of use before needing to be recharged was recorded. Company A toothbrushes operated for an average of 119.7 hours with a standard deviation Of 1.74 hours; Company B toothbrushes operated for an average of 120.6 hours with a Standard deviation of 1.72 hours. The 90% confidence interval is (-1.93, 0.13). The correct Interpretation is

Data were collected on annual personal time (in hours) taken by a random sample of 16 women and 7 men employed by a medium-sized company. The women took an average of 24.75 hours of personal time per year with a standard deviation of 2.84 hours. The men took an average of 21.86 hours of personal time per year with a standard deviation of 3.29 hours. The Human Resources Department believes that women tend to take more personal time than men because they tend to be the primary child care givers in the family. -Write the null and alternative hypotheses.

Data were collected on annual personal time (in hours) taken by a random sample of 16 women and 7 men employed by a medium sized company. The women took an average of 24)75 hours of personal time per year with a standard deviation of 2.84 hours. The men Took an average of 21.89 hours of personal time per year with a standard deviation of 3.29 Hours. The Human Resources Department believes that women tend to take more personal Time than men because they tend to be the primary child care givers in the family. The t- Test for two means is appropriate in this situation because

Data were collected on annual personal time (in hours) taken by a random sample of 16 women and 20 men employed by a medium-sized company. The women took an average Of 24.75 hours of personal time per year with a standard deviation of 2.84 hours. The men Took an average of 20.5 hours of personal time per year with a standard deviation of 2.75 Hours. The pooled estimate of the variance is

Data were collected on annual personal time (in hours) taken by a random sample of 16 women and 7 men employed by a medium sized company. The women took an average of 24.75 hours of personal time per year with a standard deviation of 2.84 hours. The men took an average of 21.89 hours of personal time per year with a standard deviation of 3.29 hours. The correct 90% confidence interval for the difference between women and men in the average number of hours of personal time taken per year is

Data were collected on annual personal time (in hours) taken by a random sample of 16 women and 7 men employed by a medium sized company. The women took an average of 24)75 hours of personal time per year with a standard deviation of 2.84 hours. The men Took an average of 21.89 hours of personal time per year with a standard deviation of 3.29 Hours. The standard error of the sampling distribution for the difference between the two Means is

Use the following for questions An army depot that overhauls ground mobile radar systems is interested in improving its processes. One problem involves troubleshooting a particular component that has a high failure rate after it has been repaired and reinstalled in the system. The shop floor supervisor believes that having standard work procedures in place will reduce the time required for troubleshooting this component. Time (in minutes) required troubleshooting this component without and with the standard work procedure is recorded for a sample of 19 employees. Does this sample indicate that having a standard work procedure in place reduces troubleshooting time? Without Standard Work Procedure With Standard Work Procedure Difference Without - With 142 119 23 144 118 26 153 126 27 148 119 29 146 121 25 149 125 24 138 116 22 145 120 25 153 124 29 160 138 22 163 135 28 170 144 26 169 142 27 151 128 23 152 131 21 167 141 26 164 140 24 165 140 25 163 138 25 -Write the null and alternative hypotheses.

Create and interpret a 90% confidence interval.

We want to know whether people are likely to offer a different amount for used exercising equipment when buying from a friend than when buying from a stranger. We wonder whether the difference between mean amounts is zero. We have bid prices from 8 subjects buying from a friend and 7 subjects buying from a stranger, found in a randomized experiment. A. What assumptions can we make? b. What type of test can we perform?

Use the following for questions An army depot that overhauls ground mobile radar systems is interested in improving its processes. One problem involves troubleshooting a particular component that has a high failure rate after it has been repaired and reinstalled in the system. The shop floor supervisor believes that having standard work procedures in place will reduce the time required for troubleshooting this component. Time (in minutes) required troubleshooting this component without and with the standard work procedure is recorded for a sample of 19 employees. Does this sample indicate that having a standard work procedure in place reduces troubleshooting time? Without Standard Work Procedure With Standard Work Procedure Difference Without - With 142 119 23 144 118 26 153 126 27 148 119 29 146 121 25 149 125 24 138 116 22 145 120 25 153 124 29 160 138 22 163 135 28 170 144 26 169 142 27 151 128 23 152 131 21 167 141 26 164 140 24 165 140 25 163 138 25 -Create and interpret a 95% confidence interval.

Use the following for questions A mid-sized company has decided to implement an enterprise resource planning (ERP) system, and management suspects that many of its employees are concerned about the planned implementation. Managers are considering holding informational workshops to help decrease anxiety levels among employees. To determine whether such an approach would be effective, they randomly select 16 employees to participate in a pilot workshop. These employees were given a questionnaire to measure anxiety levels about ERP before and after participating in the workshop. Do the data indicate that anxiety levels about ERP decreases as a result of the workshop? Pre-workshop anxiety level 7 6 9 5 6 7 5 7 6 4 3 2 1 3 4 2 Post-workshop anxiety level 4 3 7 3 4 5 4 6 5 3 2 2 1 3 4 3 Difference (Post - Pre) -3 -3 -2 -2 -2 -2 -1 -1 -1 -1 -1 0 0 0 0 1 Determine whether two samples are independent or paired. -Based on the test statistic and its P-value, state your conclusion using α = .05.

Create and interpret a 90% confidence interval.

A mid-sized company has decided to implement an enterprise resource planning (ERP) system, and management suspects that many of its employees are concerned about the Planned implementation. Managers are considering holding informational workshops to Help decrease anxiety levels among employees. They randomly select 16 employees to Participate in a pilot workshop. These employees were given a questionnaire to measure Anxiety levels about ERP before and after participating in the workshop. If we let d = post-workshop anxiety level - pre-workshop anxiety level, the correct alternative hypothesis to determine if this approach was successful is

Data were collected on annual personal time (in hours) taken by a random sample of 16 women and 7 men employed by a medium-sized company. The women took an average of 24.75 hours of personal time per year with a standard deviation of 2.84 hours. The men took an average of 21.86 hours of personal time per year with a standard deviation of 3.29 hours. The Human Resources Department believes that women tend to take more personal time than men because they tend to be the primary child care givers in the family. -Are the assumptions and conditions for carrying out the t-test for two means satisfied? Explain.

Use the following for questions A mid-sized company has decided to implement an enterprise resource planning (ERP) system, and management suspects that many of its employees are concerned about the planned implementation. Managers are considering holding informational workshops to help decrease anxiety levels among employees. To determine whether such an approach would be effective, they randomly select 16 employees to participate in a pilot workshop. These employees were given a questionnaire to measure anxiety levels about ERP before and after participating in the workshop. Do the data indicate that anxiety levels about ERP decreases as a result of the workshop? Pre-workshop anxiety level 7 6 9 5 6 7 5 7 6 4 3 2 1 3 4 2 Post-workshop anxiety level 4 3 7 3 4 5 4 6 5 3 2 2 1 3 4 3 Difference (Post - Pre) -3 -3 -2 -2 -2 -2 -1 -1 -1 -1 -1 0 0 0 0 1 Determine whether two samples are independent or paired. -Are the assumptions and conditions for carrying out the paired t-test satisfied? Explain.