211 Each day at a large hospital several hundred laboratory

2.11 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:

LAB TESTS

PERFORMED                                               SHIFT

                                                      Day        Evening                Total

Nonconforming                            16             24                         40

Conforming                                 654          306                        960

Total                                             670         330                        1,000

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?

Solution