1. Statistically-Based Quality Improvement
Chapter 12
Statistically-Based Quality Improvement
for Attributes

2. Strategic Quality Planning Statistically-Based Quality Improvement for Attributes Chapter 12
Types of attributes
Generic process for developing attribute charts
Understanding attribute charts
Choosing the right attributes chart
Reliability models

3. Strategic Quality Planning Statistically-Based Quality Improvement for Attributes Types of Attributes
Types of Attributes
Structural
Sensory
Performance
Temporal
Ethical

4. Strategic Quality Planning Statistically-Based Quality Improvement for Attributes Generic process for developing attribute charts
Identify Critical Operations
Identify critical product characteristics
Determine whether the product characteristics is a variable or an attribute

5. Strategic Quality Planning Statistically-Based Quality Improvement for Attributes Generic process for developing attribute charts
Select the appropriate process chart
Establish control limits
Update the limits when changes have been made to the process

6. Strategic Quality Planning Statistically-Based Quality Improvement for Attributes Understanding Attribute Charts
Attribute Charts deal with binomial and Poisson processes, not measurements
Think in terms of defects and defectives rather than diameters and widths

7. Strategic Quality Planning Statistically-Based Quality Improvement for Attributes Understanding Attribute Charts
A defect is an irregularity or problem with a larger unit
The larger unit may contain many defects
Defects are countable

8. Strategic Quality Planning Statistically-Based Quality Improvement for Attributes Understanding Attribute Charts
A defective is a unit that, as a whole, is not acceptable or does not meet performance requirements
Defectives are monitored p and np charts
Defects are monitored using c and u charts

9. Strategic Quality Planning Statistically-Based Quality Improvement for Attributes Understanding Attribute Charts
A p chart is a process chart that is used to graph the proportion of items in a sample that are defective
Effective to determine when there has been a shift in the proportion defectives for a particular product or service

10. Strategic Quality Planning Statistically-Based Quality Improvement for Attributes Understanding Attribute Charts
p chart applications include:
Late deliveries
Incomplete orders
Calls not getting dial tones
Accounting transaction errors
Clerical errors on written forms
Parts that do not mate properly

11. Strategic Quality Planning Statistically-Based Quality Improvement for Attributes Understanding Attribute Charts
p charts for example 12-1

12. Strategic Quality Planning Statistically-Based Quality Improvement for Attributes Understanding Attribute Charts
Example 12-1 using excel

13. Strategic Quality Planning Statistically-Based Quality Improvement for Attributes Understanding Attribute Charts
The np chart is a graph of the number of defectives in a subgroup
The np chart requires the sample size of each subgroup be the same each time a sample is drawn
The uses for the np chart are essentially the same as the p chart

14. Strategic Quality Planning Statistically-Based Quality Improvement for Attributes Understanding Attribute Charts
np charts for example 12-2

15. Strategic Quality Planning Statistically-Based Quality Improvement for Attributes Understanding Attribute Charts
Example 12-2 using excel

16. Strategic Quality Planning Statistically-Based Quality Improvement for Attributes Understanding Attribute Charts
The c chart is a graph of the number of defects per unit
The units must be of the same metric .. size, height, length, volume …
The c chart is used to detect nonrandom events in the life of a production process

17. Strategic Quality Planning Statistically-Based Quality Improvement for Attributes Understanding Attribute Charts
c chart

18. Strategic Quality Planning Statistically-Based Quality Improvement for Attributes Understanding Attribute Charts
The u chart is a graph of the average number of defects per unit.
The units can be of different Sizes, height, length, volume …

19. Strategic Quality Planning Statistically-Based Quality Improvement for Attributes Understanding Attribute Charts
u chart

20. Strategic Quality Planning Statistically-Based Quality Improvement for Attributes Understanding Attribute Charts
c and u charts using excel

21. Strategic Quality Planning Statistically-Based Quality Improvement for Attributes Choosing the Right Attributes Chart

22. Strategic Quality Planning Statistically-Based Quality Improvement for Attributes Reliability Models
Bathtub shaped function
The vertical axis is the failure rate
The horizontal axis is time
Shows products are
more likely to fail either
early or late in their
useful lifetimes

23. Strategic Quality Planning Statistically-Based Quality Improvement for Attributes Reliability Models
Series reliability
Components are in a series if the performance of the entire system depends on all the components functioning properly
The components need not be physically wired sequentially
All parts must function for the system to function

24. Strategic Quality Planning Statistically-Based Quality Improvement for Attributes Reliability Models
Parallel reliability
High reliability systems often require extremely require high component reliability
When it is impossible an alternative is to use a backup system
Another word for backup is redundant or parallel

25. Strategic Quality Planning Statistically-Based Quality Improvement for Attributes Reliability Models
Measuring reliability
Failure rate = l = number of failures>(units tested * number of hours tested)
Mean Time to failure =
Mean Time Between Failures = total operating hours>number of failures

26. Strategic Quality Planning Statistically-Based Quality Improvement for Attributes Reliability Models
System Availability
System availability = MTBF>(MTBF + MTTR)

27. Strategic Quality Planning Statistically-Based Quality Improvement for Attributes Summary
Types of attributes
Generic process for developing attribute charts
Understanding attribute charts
Choosing the right attributes chart
Reliability models

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Printed in the United States of America.