Page 275 - Lean six sigma demystified

Chapter 8 SuStaining impr ovement 253

• Trying to show too much detail on any one flowchart. Use macro- and
microlevel flowcharts to describe increasing levels of detail.
• Using internal efficiency indicators rather than external effectiveness
indicators based on customer requirements.

Control Charts for Sustaining improvement

Most service businesses will use two main control charts—the individuals and
moving range (XmR chart) for cycle times and ratios, and fraction defective
chart (p chart). Manufacturing businesses will often use the XbarR, XmR, p, or
u charts. Other applications include

• Financial—XmR charts of expenses, revenues, and so on
• Customer satistfaction—XmR chart of percentage satisfied

• Call centers—XmR of wait times, p chart of abandoned calls
• Growth—XmR and p charts

Using the QI Macros Control Chart Wizard, you can just select your data
and let the Wizard choose the chart for you.
? still struggling

Control charts can detect subtle process shifts that can’t be detected with the

five senses. Once a process improves beyond 3-Sigma, it’s almost impossible to
detect process shifts without them. Control charts are so easy to draw with the
QI Macros that anyone can do it. Then it’s just a matter of analyzing the results
to detect process problems.

Stability and Capability

In Chap. 6, we looked at how to measure process capability using histograms.
To access capability, however, the process must be in statistical process control.
If the process is both stable and capable, just keep monitoring. If not, it’s time
to crank up some improvement efforts: