Six Sigma and The Empirical Rule

["Van Putten, Dirk" <Dvanputten@lodanwest.com>]

Hello Denizen's:

Here is a rookie statistics questions so please go easy on me.

Does the term "Six Sigma" refer to a total data dispersion range of 6 sigma
centered about the mean on a normally distributed sample? Or does "Six
Sigma" refer to a one-sided data spread (either to the right or left of the
mean) for a total of 12 sigma data dispersion range?

The Empirical Rule states that at 3 standard deviations (sigma for a sample)
to the right and left (total dispersion range of 6 sigma), 99.73% of all
data should fall within that range.

If "Six Sigma" refers to a dispersion range of 12 sigma, what does the
Empirical Rule state at 6 standard deviations? Does anyone have a reference
for the application of the Empirical Rule past 3 standard deviations? I
looked at 3 statistics books and they only go up to 3 standard deviations.

Thank you, Dirk van Putten
dvanputten@lodanwest.com