An experiment was performed to investigate the effectiveness of five insulating materials. Four samples of each material were tested at an elevated voltage level to accelerate the time to failure. The failure times (in minutes) are shown below:

Material Failure Time (minutes)

1 110 157 194 178 2 1 2 4 18 3 880 1256 5276 4355 4 495 7040 5307 10,050 5 7 5 29 2

(a) Do all five materials have the same effect on mean failure time?

(b) Plot the residuals versus the predicted response. Construct a normal probability plot of the residuals. What information is conveyed by these plots?

(c) Based on your answer to part (b), conduct another analysis of the failure time data and draw appropriate conclusions.