1. The Certified Quality Engineer Handbook Examples from Ch
The Certified Quality Engineer Handbook Examples from Ch. 37: Statistical Process Control (SPC)
Dr. Joan Burtner
Certified Quality Engineer
Associate Professor of
Industrial Engineering and Industrial Management

2. Quality as a System Characteristic
Goal: A stable Quality Management System (QMS) with well-defined policies and procedures and a culture of compliance with those procedures.
System Characteristics:
System Out of Control
One or more processes exhibit special causes.
System in Control
There is no evidence of special causes within the system.
Improved System in Control
Stable processes are continuously being improved.
Source : Dean (2013) Lean Healthcare Deployment and Sustainability
ISE 428 ETM 591 JMB CH 37 Examples
Spring 2014

3. Borror: Chapter 37 Review of Charts
Construction of Control Charts
Control Charts for Attributes
Control Charts for Variables
Interpretation of Control Charts
“Manual” Application of Tests
Statistical Software Application of Tests
Other Process Charts
ISE 428 ETM 591 JMB CH 37 Examples
Spring 2014

4. Control Limits, Random and Nonrandom Sample Observations
Upper
Control
Limit
(UCL)
Non-random
Non-random
+3σ
Process
Mean
99.7%
Lower
Control
Limit
(LCL)
-3σ 1 2 3 4 5 6 7 8 9 10 11 12
Sample number
Source: Ozcan Figure (Modified for Three Sigma Limits)
ISE 428 ETM 591 JMB CH 37 Examples
Spring 2014

5. Statistical Control Chart Types
Attributes
Variables(Subgroups)
c-chart
p-chart
u-chart
Mean Charts
(X-bar Charts)
Variation Charts
σ Method
Range Method
ISE 428 ETM 591 JMB CH 37 Examples
Spring 2014

6. Variables Control Charts (Continuous Data)
When process characteristics can be measured, variables control charts are the appropriate way to display the process monitoring.
The Xbar-chart and the Range chart are displayed and interpreted together.
When the Range chart exhibits out-of-control status, the rules for evaluating the Xbar-chart should not be used.
The Xbar chart is appropriately evaluated after the Range chart indicates that the process is in control. Use caution in interpretation when using statistical software that evaluates both charts simultaneously.
See examples on pages
ISE 428 ETM 591 JMB CH 37 Examples
Spring 2014

7. Variables Control Chart for n = 1
Variables(Subgroups)
Variables (Individuals)
Individual observation
Moving Range
Mean Charts
(X-bar Charts)
Variation Charts
Note that the tests that apply to the subgroup charts do not apply to the Individuals Charts.
σ Method
Range Method
ISE 428 ETM 591 JMB CH 37 Examples
Spring 2014

8. Attribute Control Charts (Discrete Data)
When process characteristics can be counted, attribute-based control charts are the appropriate way to display the process monitoring.
The p-chart is the appropriate control chart for a process with only two outcomes (defective or not defective) when the proportion defective is calculated.
The c-chart is the appropriate tool to display monitoring if the number of occurrences per sampling period is recorded.
The u-chart is the appropriate control chart if the number of occurrences and the number of items per sampling period is recorded. The average number of occurrences per sample is calculated.
ISE 428 ETM 591 JMB CH 37 Examples
Spring 2014

9. Attribute Control Charts (Discrete Data)
See text for examples of p-chart.
See text for examples of c-chart.
We will discuss the u-chart example in class.
ISE 428 ETM 591 JMB CH 37 Examples
Spring 2014

10. Borror: Example 37.4
A random sample of 1000 account activities is collected weekly for 12 weeks. The institution would like to monitor the proportion of errors.
Week
Activities in Error 1 6 7 9 2 11 8 3 4 12 10 5 30
ISE 428 ETM 591 JMB CH 37 Examples
Spring 2014

11. 37.4 Chart Construction and Analysis
Are the data discrete or continuous?
Discrete
Do the data fit the requirements of a p , c, or u chart?
p chart
What tests for special causes apply to this type of chart?
Extreme point, trend, shift in mean, oscillation
Zone rules (A,B,C) do not apply to p charts
ISE 428 ETM 591 JMB CH 37 Examples
Spring 2014

12. 37.4 Chart Analysis Original control chart produced using Minitab 15
Evidence of special cause (extreme point)
ISE 428 ETM 591 JMB CH 37 Examples
Spring 2014

13. 37.4 Process Improvement
Assignable cause is identified for the out of control point.
Sample point 6 is eliminated and a new control chart is produced using Minitab 15.
ISE 428 ETM 591 JMB CH 37 Examples
Spring 2014

14. *******Pre-control Charts *******
Other Charts
Cumulative Sum Charts
EWMA Charts
Moving Average Charts
*******Pre-control Charts *******
ISE 428 ETM 591 JMB CH 37 Examples
Spring 2014

15. References / Contact Information
Borror, C, Ed. (2009). The Certified Quality Engineer Handbook 3rd edition, Milwaukee, WI: ASQ Quality Press.
Dean, M.L. (2013). Lean Healthcare Deployment and Sustainability. New York, NY: McGraw Hill.
Ozcan, Y. (2009). Quantitative Methods in Health Care Management 2nd ed, San Francisco, CA: Jossey-Bass.
Contact Information:
Dr. Joan Burtner
ISE 428 ETM 591 JMB CH 37 Examples
Spring 2014