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### Six Sigma

#### What is Six Sigma

• a statistical measure of process capability

• a set of tools and techniques for reducing variation

• a philosophy about operational excellence

• A Measurement Scale which compares the output
of a process to customer requirements

#### Its all about continuous improvement by reducing variation

###### What is Variation
• as a customer you want consistency in any product or service that you consume

• variation causes dissatisfaction or defect

• defect - any thing that doesnt meet customer expectation

• we generally measure process performance as an average v/s some target

• average would hide the variation between data points

• example - average of 4 cars' speed 25, 50 , 75 & 100 is 62.5 , does this show or hide the difference between each car ?

• So variation should be measured

• we measure variation via (depending on the data distribution)

• Standard deviation ​

• Range

• Inter quartile range

###### Basic premises underlying six sigma
• All processes have variability

• Variability has definable causes

• Typically only a few causes are significant

• If causes can be identified & understood, they can be controlled

• Design must be robust to the effects of remaining process variations

###### 6 sigma a measure of performance
• 6 sigma = 6 σ ; σ is Greek letter s

• σ denotes standard deviation - average distance of data points in a set from the mean (average)

• Standard deviation shows variation from mean & your mean should be near or on the target

• Smaller the standard deviation ; lesser the variation

• So if your data sets' variation, denoted by σ,  is small enough, you would be able to put 6 σ (six std deviations) between the target and customer specifications

• This can also be denoted as DPMO - defects per million opportunities ; so 3.4 DPMO would denote a 6σ level performance

• 3.4 DPMO = 99.99666% = 6σ

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