Insulating fluid breakdown. Use the data in Table 4.1.
Combine groups 1 and 2, 3 and 4, and 5 and 6 to get three new groups, each with
20 times to breakdown. Assume that such times have an exponential distribution,
and check for stability of the data over time as follows.
(a) Calculate the estimate of the mean for each of the three
groups. How many degrees of freedom does each estimate have?
(b) Calculate the pooled estimate of the assumed common
(c) Calculate Bartlett’s test statistic (4.6) for the three
groups. How many degrees of freedom does it have?
(d) Look up 90 and 95% points of the corresponding
chi-square distribution. Do the three sample means differ statistically
significantly? If so, why?
(e) Calculate simultaneous approximate 90% confidence limits
for all ratios of pairs of the three means. Are any ratios wholly statistically