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Standard Deviation

Dispersion of data is important. In Quality field, dispersion is important factor to succeed.
Standard deviation and variance ( square of standard deviation ) are useful Statistical Value to evaluate dispersion.

Coefficient of variation

There is a case that standard deviation is larger as average is larger. In such case, standard deviation is not appropriate to evaluate.

Coefficient of variation is defined as
"Standard deviation / average"
This is useful to solve problem.

SN ratio of Quality Engineering

SN ratio series of Quality Engineering is also made to evaluate dispersion.

NEXT Standard Error