Six Sigma

  • Six Sigma is a statistical approach which aims to drive up profits by putting special effort into ensuring goods or services conform to specification
  • As with SPC, it’s applicable to repetitive, relatively simple processes – but some goods and service organisations need much higher precision with their outputs if they are to meet acceptable standards for reliability or service
  • Hence, it’s not only about eliminating unpleasant surprises and broken promises via:
    • Reducing any variation in the outputs from processes – defects or delivery times say – by ensuring virtually all meet certain minimum standards
    • Reducing waste and inefficiency
    • Redesigning a company’s products and internal processes so that customers get what they want, when they want and when they were promised
  • But getting things right 95% of the time is just not good enough if one has thousands of customers or more:
    • Deliveries to homes must be made when customers are in and waiting, not an hour or two later when they’ve had other appointments
    • Personal computers must work every time when millions switch them on, not 99 times out of 100
    • Airlines must not lose luggage
    • Hospitals must not make mistakes with in-patients  
  • Six Sigma is thus Statistical Process Control with extremely strict control limits:
    • SPC usually requires some 99.97% of the output from any process to fall within three standard deviations of the average – in other words 0.03% (3 defective items in every 10,000) may fall outside this range
    • Six Sigma aims for no more than 3.4 defects per million – covered by a range of 6 standard deviations from the average
  • The latter maximum failure rate is vital for a company like Intel – imagine if you bought a computer which often didn’t work because of a dodgy chip they’d made


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