Six Sigma, Pyramids and Systems

A 'sigma' refers to the standard deviation from the mean of a population. Standard deviation indicates the likelihood that your next data point will deviate from the mean of the data set.
At the bottom of the Six Sigma pyramid begins a system’s current process capability. Usually at 1 or 2 Sigma levels is “tribal” knowledge based on first-time experiences. An organization moves up the pyramid to 3 Sigma as systems are put in place. To hit 4 Sigma, statistics and modeling tools are used for significant process improvement. And, finally, to aim for that near perfection, organizations apply DFSS, or Design for Six Sigma.