Question

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).

Statistic	Test Group					Control Group
Mean Damage	X¯¯¯1X¯1	=	$	1,157		X¯¯¯2X¯2	=	$	1,775
Sample Std. Dev.	s1	=	$	662		s2	=	$	827
Repair Incidents	n1	=		17		n2	=		13

(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 --- to ----

(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 --- to ---

Answer 1

Please LIKE if it really helps you!!!