and it is one of the most common in statistics.
             [pic]
             The two parameters that define this function are the mean and the
             standard deviation, also referred to as sigma. The standard deviation
             measures how far from the mean average value the values of the distribution
             have deviated. The function covers +/- 6 sigmas from the process mean,
             hence the name of the process. The idea of the Six Sigma process is how to
             cover the whole span of customer specifications (as identified with the
             Gauss function), that is the whole +/- 6 sigmas of the process. Notice,
             however, that the +/-6 sigmas cover only 99.99999% of the process, which
             means there is always room for improvement. We can conclude from this
             theoretical presentation that Six Sigma is "a measure of customer
             satisfaction that is near perfection"[4]- the sigma actually measures how
             far from the customer requirements the company has deviated, in terms of
             number of dissatisfied customers for one million customers. As a
             ...