To evaluate the difference in the reliability of cooling motors for PCs from two suppliers, an accelerated life test is performed on 50 motors randomly selected from the warehouses of the two suppliers. Supplier A's motors are considerably more expensive in comparison to the motors of supplier B. Of the motors from supplier A, 37 were still running at the end of the test period, whereas only 27 of the 50 motors from supplier B were still running at the end of the test period.
a. Is there significant evidence that supplier A's motors are more reliable than supplier B's motors? Use α = .05 .
b. Use the Fisher exact test to test the research hypothesis that supplier A's motors are more reliable than supplier B's motors. Compare your conclusions with the conclusions reached in part (a).
c. Calculate 95% confidence intervals for the proportion of motors that passed the test for each supplier and for the difference in the two proportions. Interpret the results carefully in terms of the reliability of the two suppliers.