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 mean.
(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 significant?
Table 4.1
