Each day at a large hospital, several hundred laboratory tests are performed. The rate at which these tests are done improperly (and therefore need to be redone) seems steady, at about 4%. In an effort to get to the root cause of these nonconformances, tests that need to be redone, the director of the lab decided to keep records over a period of one week. 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 Nonconforming Conforming Total Day Evening Total 24 654 306960 330 16 40 670 1 ,000