six sigma green belt part 22-2 variation • the study of variation begins with a review of the...

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Six Sigma Green Belt

Part 2

Variation

© 2013 IIE and Aft Systems, Inc.

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Variation

• The study of variation begins with a review of the teachings of W. Edwards Deming

• Dr. Deming proposed a theory, the Theory of Profound Knowledge, that he stated was essential for any organization that desired to be competitive in today’s marketplace

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Profound Knowledge

• Knowledge of Systems

(Processes)

• Knowledge of Statistics (Variation)

• Knowledge of Psychology (Motivation)

• Knowledge of Knowledge

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Knowledge of Systems

1. A system is a network of interdependent components that work together to try to accomplish an aim

2. Systems are management’s responsibility

3. Management’s job is to optimize the entire system over time

© 2013 IIE and Aft Systems, Inc.

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Variation

• Variation happens — it is the voice of the system or process

• Use statistics to make the invisible visible — show patterns and types of variation

• Distinguish between special and common causes of variation

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Variation

• Must act according to type of cause and avoid tampering

• Shrink, shrink, shrink variation — reducing variation reduces costs

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When people do not

understand variation

See trends where there are no trends

Blame and give credit to others for things over

which they have little or no control

Build barriers, decrease morale, and create an

atmosphere of fear

Never be able to fully understand past

performance, make predictions about the

future and make significant improvements in

processes

© 2013 IIE and Aft Systems, Inc.

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Psychology Theory of Motivation

• People want to do a good job, contribute, and have pride and joy in their work

• Need to tap into intrinsic motivation

• Must drive out fear and build trust

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Knowledge of Knowledge

Rational prediction requires theory and we build knowledge through systematic revision and comparison of theory based on comparison of prediction with observation.

Which means we must capture that theory.

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Variation

Everything varies

Nothing is exactly 100 percent repeatable That is the way things normally occur

To illustrate this we will do the following

exercise using a process in which each of

you is the world’s expert

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Exercise

On this page sign your name as you normally would.

__________________

__________________

__________________

__________________

__________________

__________________

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Types of Variation

Common Cause

Refer to situations, usually within those systems and processes that are more ongoing, chronic, and persistent.

Special Cause

Refer to sentinel events, one-time occurrences, or other unique out-of-the-ordinary circumstance.

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About Variation

• Special Cause

– Find special causes and address

• Prevent

• Contingency plan

– Those closest to the process are most likely to find the special causes of variation

• Common Cause

– Take action on the system

– Management is responsible for the system

© 2013 IIE and Aft Systems, Inc.

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Stable Process

• When only normal variation is present in a process the process is said to be stable

• Stable processes are predictable

• Stable processes are in (statistical) control

• Stable processes have a known process capability

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Control

A process is said to be in statistical control when, through the use of past experience, we can predict how the process will vary in the future

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Theorem

• Basic Theorem of Variation

• Corollary to the Basic Theorem of Variation

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Dr. Deming’s School Bus

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About Variation

• Special Cause

– Find special causes and address

– Those closest to the process are most likely to find the special causes of variation

• Common Cause

– Take action on the system

– Management is responsible for the system

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Process Monitoring

In order to monitor any process effectively there are several pieces of information that must be known:

– Central location

– Spread

– Shape

– Relationship of variation to time

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Data Collection Exercise

2 3 4 5 6 7 8 9 10 11 12

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What Can We Learn About

• Location

– Process centered

– Process requirement

• Spread

– Observed

– Specifications

• Shape

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Histograms

A histogram is a graphical representation of data in a bar chart format. Histograms are also used to observe the “shape” of data.

© 2013 IIE and Aft Systems, Inc.