Suppose that the medical staff indicates that the results of a given laboratory procedure must be available 30 minutes after the physician submits a request for the service. In this situation, if the results arrived 30 minutes or less after the request, we regard the performance of the laboratory as timely. If results arrived more than 30 minutes after the request, we regard the performance as tardy. Focusing on the day, evening, and night shifts, suppose that we selected a random sample and obtained the following results:

Shifts

Performance     Day     Evening    Night

Timely                   100         80          40

Tardy                     20           30           40

If a = 0.05, use the results to test the proposition that the performance of the laboratory is independent of shift.