Insulating oil. An experiment on breakdown voltage of an insulating oil used two electrode diameters and three rates of rise of voltage (in V/second)-six test conditions in all. Theory assumes that each distribution of breakdown voltage is Weibull, the scale parameter ak depends on the test condition, but the shape is a constant ß. For each test condition, there were 60 breakdown voltages. Separate Weibull fits to the six data sets yielded the following.

For the model with a common shape parameter, the results are

(a) Calculate the log likelihood ratio test statistic for equality of the six shape parameters.

(b) How many degrees of freedom does this statistic have?

(c) Do the shape parameters differ statistically significantly? In Section 4, they have a wholly significant difference at the 5% level.

(d) Make a normal probability plot of the ­ and determine how the shape parameters differ.