Monitoring surgery complications. An article on the use of control charts for monitoring the proportion of post operative complications at a large hospital was published in the International Journal for Quality in Health Care (October 2010). A random sample of surgical procedures was selected each month for 30 consecutive months, and the number of procedures with postoperative complications was recorded. The data are listed in the accompanying table. Of the total of 2,939 procedures sampled, 294 had complications.

a. Identify the attribute of interest to the hospital.

b. What are the rational subgroups for this study?

c. Find the value of p for use in a p-chart.

d. Compute the proportion of post-op complications in each month.

e. Compute the critical boundaries for the p-chart (i.e., UCL, LCL, Upper A–B boundary, etc.).

f. Construct a p-chart for the data. g. Interpret the chart. Does the process appear to be in control? Explain. Month: 1 2 3 4 5 6 7 8 9 10 Procedures: 105 97 115 100 95 111 68 47 83 108 Complications: 14 12 10 12 9 7 9 11 9 12 Month: 11 12 13 14 15 16 17 18 19 20 Procedures: 115 94 107 99 105 110 97 105 71 48 Complications: 10 7 12 9 15 13 7 10 8 5 Month: 21 22 23 24 25 26 27 28 29 30 Procedures: 95 110 103 95 105 100 116 110 105 120 Complications: 12 9 7 9 25 12 8 2 9 10