Each day at a large hospital, hundreds of laboratory tests are performed. The rate of "non conformances," tests that were done improperly (and therefore need to be redone), has seemed to be steady, at about 4%. In an effort to get to the root cause of the non conformances, the director of the lab decided to study the results for a single day. The laboratory tests were subdivided by the shift of workers who performed the lab tests. The results are as follows:

a. Construct contingency tables based on total percentages, row percentages, and column percentages.
b. Which type of percentage-row, column, or total-do you think is most informative for these data? Explain.
c. What conclusions concerning the pattern of nonconforming laboratory tests can the laboratory director reach?

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SHIFT LAB TESTS PERFORMED Day Evening Total 40 16 306 Nonconforming Conforming Total 654 3 960 670 330 1,000