Statistical

1
Chapter 11

• Statistical
• Thinking and
• Applications

2
Statistical Thinking

• All work occurs in a system of interconnected
  processes
• Variation exists in all processes
• Understanding and reducing variation are the keys
  to success

3
Sources of Variation in Production Processes
Measurement Instruments
Operators
Methods
Materials
INPUTS
PROCESS
OUTPUTS
Tools
Human Inspection Performance
Environment
Machines
4
Variation

• Many sources of uncontrollable variation exist
  (common causes)
• Special (assignable) causes of variation can be
  recognized and controlled
• Failure to understand these differences can
  increase variation in a system

5
Key Idea
A system governed only by common causes is called
a stable system. Understanding a stable system
and the differences between special and common
causes of variation is essential for managing any
system.
6
Problems Created by Variation

• Variation increases unpredictability.
• Variation reduces capacity utilization.
• Variation contributes to a bullwhip effect.
• Variation makes it difficult to find root causes.
  
• Variation makes it difficult to detect potential
  problems early.

7
Two Fundamental Management Mistakes

1. Treating as a special cause any fault, complaint,
   mistake, breakdown, accident or shortage when it
   actually is due to common causes
2. Attributing to common causes any fault,
   complaint, mistake, breakdown, accident or
   shortage when it actually is due to a special
   cause

8
Do it right the first time!
Take Pride in Your Work!
Be a Quality Worker!
9
Lessons Learned

• Quality is made at the top.
• Rigid procedures are not enough.
• People are not always the main source of
  variability.
• Numerical goals are often meaningless.
• Inspection is expensive and does not improve
  quality.