In the book Tools and Methods for the Improvement of Quality, Gitlow, Gitlow, Oppenheim, and Oppenheim discuss a data entry operation that makes a large number of entries every day. Over a 24-day period, daily samples of 200 data entries are inspected. Table 17.12 gives the number of erroneous entries per 200 that were inspected each day.
a. Use the data in Table 17.12 to compute . Then use this value of  to calculate the control limits for a p chart of the data entry operation, and set up the p chart. Include zone boundaries on the chart.
b. Is the data entry process in statistical control, or are assignable causes affecting the process? Explain.
c. Investigation of the data entry process is described by Gitlow, Gitlow, Oppenheim, and Oppenheim as follows:
In our example, to bring the process under control, management investigated the observa-tions which were out of control (days 8 and 22) in an effort to discover and remove the special causes of variation in the process. In this case, management found that on day 8 a new operator had been added to the workforce without any training. The logical conclusion was that the new environment probably caused the unusually high number of errors. To ensure that this special cause would not recur, the company added a one-day training program in which data entry operators would be acclimated to the work environment.
A team of managers and workers conducted an investigation of the circumstances occurring on day 22. Their work revealed that on the previous night one of the data entry consoles malfunctioned and was replaced with a standby unit. The standby unit was older and slightly different from the ones currently used in the department. The repairs on the regular console were not expected to be completed until the morning of day 23. To correct this special source of variation, the team recommended purchasing a spare console that would match the existing equipment and disposing of the outdated model presently being used as the backup. Management then implemented the suggestion.
Since the assignable causes on days 8 and 22 have been found and eliminated, we can remove the data for these days from the data set. Remove the data and calculate the new value of P. Then set up a revised p chart for the remaining 22 subgroups.
d. Did the actions taken bring the process into statistical control? Explain.