Exam 20: Introduction to Quality and Statistical Process Control

The control limits in the x-bar chart are set so that 95 percent of the values will fall inside the control limits when there is only common cause variation.

One of the roles of managers who are overseeing the statistical process control analysis is to set the control limits at the desired levels prior to collecting data from the process.

A p-chart is useful for:

Which of the following process changes cannot be detected with a process control chart?

Common cause variation is variation in the output of a process that is unexpected and has an assignable cause.

A stable process is one that has had all its variation removed through quality improvement efforts on the part of the organization.

The statistical process control (SPC) chart is one of the most important tools for identifying important issues to improve quality.

A major airline is interested in monitoring customer satisfaction with its baggage handling process. To do so, each day the airline randomly selects 100 customers and surveys them to determine if they are satisfied or not with the service provided. After 20 samples, a total of 260 unsatisfied customers were surveyed. a. If the airline wishes to use a control chart, which chart would you recommend and why? b. Determine the 3-sigma control limits for the appropriate control chart.

A process control chart can be used to determine whether the process average has shifted up or down, but is not useful for determining whether the process is just drifting in an upward or downward direction.

Referring to the SPC chart signals that a process is out of control, what type of problem does each signal indicate? List the signals.

The issue with a process always involves a quantitative variable.

Control charts monitor a process as it currently operates, not necessarily how you would like it to operate.

Identify the four primary signals that indicate a change and that, if observed, will cause us to reject the null hypothesis. State the probability of a Type I error for this definition.

A plywood manufacturer is interested in monitoring the thickness of the plywood. Which of the following would be most useful for doing this?

If a process control chart has only one point outside the upper or lower control limits, there is insufficient evidence to conclude that the process was out of control at the time that the measurement was taken.

A stable process is typically defined as one in which all output is operating within ± 3 standard deviations of the process center.

Each evening, a nationwide retail chain randomly calls 100 of the customers who came to their store that day to ask whether they were satisfied with the service they had received. The customers respond yes or no. Suppose the company has found over time that 8 percent of the customers are not satisfied ("no" answers), what is the 3-sigma upper and lower control limits for the appropriate control chart?

The main process change that can be detected with a process control chart is:

We expect virtually all the data in a stable process to fall within 2 standard deviations of the mean.

Each evening, a nationwide retail chain randomly calls 100 of the customers who came to their store that day to ask whether they were satisfied with the service they had received. The customers respond yes or no. Suppose the company has found over time that 8 percent of the customers are not satisfied ("no" answers). If they have established a process control chart, what conclusion should be reached if the percentage of customers surveyed tonight that say no is 14 percent?