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Six Sigma

  • Six Sigma is a statistical approach which aims to drive up profits by putting extra special effort into ensuring goods or services conform to specification

  • As with SPCStatistical Process Control it’s applicable to repetitive 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 by:

    • Reducing 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 99% of the time is often not good enough if one has thousands of customers:

    • 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 any of their passengers’ luggage

    • Hospitals must not make mistakes with in-patients  

  • Six Sigma is SPC – Statistical Process Control – but with much stricter control limits:

    • SPC usually requires some 99.97% of the output from any process to fall within three standard deviations of the average for customer acceptability– 0.03% may fall outside this range – 3 defective items in every 10,000

    • Six Sigma aims for no more than 3.4 defects in every 1,000,000, 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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