1. originally developed by Walter A. Shewhart
Control Charts
originally developed by
Walter A. Shewhart

2. Control Charts
The control chart is a statistical quality control tool used in the monitoring variation in the characteristics of
a product or service

3. Control Charts
The control chart focuses on the time dimension and the nature of the variability in the system.

4. Control Charts
The control chart may be used to study past performance and/or to evaluate present conditions.

5. Control Charts
Data collected from a control chart may form the basis for process improvement.

6. Control Charts

7. Control Charts UCL = Process Average + 3 Standard Deviations
LCL = Process Average - 3 Standard Deviations X
UCL
+ 3
Process Average
- 3
LCL
TIME
Levine, Prentic-Hall

8. Control Charts Graph of sample data plotted over time
Assignable Cause Variation
UCL
Process Average 
Mean
LCL
Random Variation
Levine, Prentice-Hall

9. Control Charts X X X
Common Cause Variation: no points outside control limit
Special Cause Variation: two points outside control limit
Downward Pattern: no points outside control limit; however, eight or more points in trend
Levine, Prentice-Hall

10. Control Charts
Attribute charts
Variables charts

11. be used for categorical variables.
Control Charts
Charts may
be used for categorical variables.
[i.e.: attributes]

12. Control Charts
Whenever a character of interest is measured on a nominative or an interval, ie: categorical, scale…an attributes control chart is used to monitor a process.

13. proportion [p-charts]
Control Charts
Attributes Control Charts
counts [c-chart]
proportion [p-charts]

14. when sample size are not constant
Control Charts
Attributes Control Charts
when sample size are not constant
and/or are unknown
use counts charts
[c-charts]

15. Control Charts

16. when sample size are constant and are known
Control Charts
Attributes Control Charts
when sample size are constant and are known
use proportion charts
[p-charts]

17. Control Charts

18. be used for interval or ratio data [i.e.: variables ]
Control Charts
Charts may
be used for interval or ratio data [i.e.: variables ]

19. Control Charts
Whenever a character of interest is measured on an interval or a ratio scale, a variables control chart is used to monitor a process.

20. Control Charts Variables Control Charts Mean and Range charts
[x-bar & R charts]

21. Control Charts
Variables control charts are typically used used in pairs.
…… one chart monitors process average while the other monitors the variation in a process.

22. Control Charts

23. Control Charts

24. Control Charts In conclusion:
the control chart is a means of monitoring variation in the characteristics of a product or service

25. Control Charts
Know the assumptions … let the computer do the hard work.

26. Control Charts
Questions?