What is Six Sigma?

Six Sigma is a  process improvement methodology that aims to:

·        Reduce defects to a rate of 3.4 defects per million defect opportunities,
·        By identifying and eliminating causes of variation in business processes,
·        Using statistical processes, wherever required, and 
·        Focusing on development of a very clear understanding of customer requirements
(Voice of Customer).

Focus on Causes of Variation:
From the Six Sigma viewpoint, a business process is normally represented in terms of  Y = f (X’s) in which the Output (Y) is determined by some Input variables (X’s).

* If we suspect that there is a relationship between an outcome (Y) and potential causes (X’s), we
  must collect and analyze data to prove our hypothesis.

* If we want to change the outcome, we need to focus on identifying and controlling the causes,
   rather than checking the outcomes.

* When we know enough and have good control of the X’s we can accurately predict Y.

   If this is not done, we will focus our efforts on Non Value Adding (NVA) Activities like inspection,
   testing and reworking.

Statistical Processes:

Building new measurement systems (metrics) and then asking new questions is an integral part of Six Sigma methodology.
To improve results, we need to identify ways to measure variation  in business processes, generate statistics based on those measurements and then use those statistics to ask new questions about the sources of quality problems.
Six Sigma is not a quality management system, such as ISO-9000, or a quality certification system. It is a methodology for reducing defects based on process improvement.




Six Sigma levels:
“Sigma” means standard deviation,
Therefore Six Sigma means six times the standard deviation.

   * Table: Sigma Level, Defects per Million, Defects as Percent, and Improvement:

One Sigma                       690,000.0                   69.0000%
 Two Sigma              308,000.0           30.8000%              2 times

Three Sigma                    66,800.0                      6.6800%                       5 times

Four Sigma              6,210.0                 0.6210%                10 times

Five Sigma                               230.0                       0.0230%                     30 times

Six Sigma                       3.4                   0.0003%              80 times

The objective of Six Sigma is only 3.4 defects (or errors) out of every million defect opportunities. This translates into 99.9997% perfection.
(Since most ISO-9000 certified organizations in India are currently around two or three Sigma, a process improvement project using Six Sigma principles may initially aim at Four Sigma or Five Sigma, which would still result in significant defect reduction).

* Table: Comparison of 99 % Quality Vs 99.9997 %

Activity / Operation Error (Nos.) With 99 % Quality Error (Nos.) With 99.9997 % Quality
Delivery of 300,000 letters 3,000 mis – deliveries 1 mis – deliveries
Out of 5,00,000 computer restarts 5,000 crashes < 2 crashes
For 50 years of month – end closings 6 months would not balance 0.0018 month (0.25 day)would not balance
For 7 days of TV broadcasting 1.68 hours of dead – air 1.8 secs of dead – air
Clearance of 200,000 chequesin a week    
Handling of 60,000 nos. baggage by  Airlines in a day    

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