A special bumper was installed on selected vehicles in a large fleet. The dollar cost of body repairs was recorded for all vehicles that were involved in accidents over a 1-year period. Those with the...

Extracted text: A special bumper was installed on selected vehicles in a large fleet. The dollar cost of body repairs was recorded for all vehicles that were involved in accidents over a 1-year period. Those with the special bumper are the test group and the other vehicles are the control group, shown below. Each "repair incident" is defined as an invoice (which might include more than one separate type of damage). Test Group Control Group X2 - $ 1,784 52 = $ n2 = Statistic X1 = $ 1,072 51 = $ Mean Damage Sample Std. Dev. 668 821 Repair Incidents ni = 18 15 Source: Unpublished study by Thomas W. Lauer and Floyd G. Willoughby. (a) Construct a 98 percent confidence interval for the true difference of the means assuming equal variances. (Round your final answers to 3 decimal places. Negative values should be indicated by a minus sign.) The 98% confidence interval is from (b) Repeat part (a), using the assumption of unequal variances with Welch's formula for d.f. (Round the calculation for Welch's df to the nearest integer. Round your final answers to 3 decimal places. Negative values should be indicated by a minus sign.) The 98% confidence interval is from (c) Did the assumption about variances change the conclusion? O Yes O No


Extracted text: (d) Construct separate 98% confidence intervals for each mean. (Round your intermediate terit value to 3 decimal places. Round your final answers to 2 decimal places.) Mean Damage T1 = $1,072 = $1,784 Confidence Interval ($ $ ($