The Psychology of Quality and More

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Genichi Taguchi

Taguchi is a statistician's statistician, known for extending the realm of Statistical Quality Control, particularly in Design of Experiments, with a branch now known as 'Taguchi methods'. 

Taguchi characterized products and processes in terms of factors that can be separated into two types:

  • Controllable (or design) factors (CF) are those whose values may be set or easily adjusted by the designer or process engineer. These subdivide into:
  • Target control factors (TCF) or signal factors are those which the average levels of the response of interest.
  • Variability control factors (VCF) affect the variability in the response.
  • Cost factors affect neither the mean response nor the variability and can be adjusted to fit economic requirements.
  • Uncontrollable (or noise) factors (NF), which are sources of variation often associated with the production or operational environment. Overall performance of the final product or process should be designed to be insensitive to variation in noise factors. These can be internal noise factors (from deterioration and manufacturing imperfections) or external noise factors (from operating conditions and environment).

He defined quality as:

"The loss imparted to society from the time the product is shipped."

This includes soft factors such as customer dissatisfaction, reputation etc.

His Quality Loss Function views 'in spec' as inadequate and uses a (parabolic) calculation that gives an increasing value as it approaches the central points between upper and lower specification limits.

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