Suppose as part of your job you are responsible for installing emergency lighting in a series of state office buildings. Bids have been received from four manufacturers of battery-operated emergency lights.

The costs are about equal, so the decision will be based on the length of time the lights last before failing. A sample of four lights from each manufacturer has been tested, with the following values (time in hours)

recorded for each manufacturer:

Type A Type B Type C Type D 1,024 1,270 1,121 923 1,121 1,325 1,201 983 1,250 1,426 1,190 1,087 1,022 1,322 1,122 1,121

a. Using a significance level equal to 0.01, what conclusion should you reach about the four manufacturers’ battery-operated emergency lights?

Explain.

b. If the test conducted in part a reveals that the null hypothesis should be rejected, what manufacturer should be used to supply the lights? Can you eliminate one or more manufacturers based on these data?

Use the appropriate test and a = 0.01 for multiple comparisons. Discuss.