Reduction variations is the strategy of Six Sigma approach. Standard deviation which is a square root of variance is the measure of variations. The approach is to reduce the sigma value and the better process experience.

However , there are two other types of variations, namely, Operator origin variations ...measured as Reproducibility and Guage variations ...repeatability is another element of Guage variations coming from operator origin.Measurement system analysis deals withis types of variations.

There is another aspect of looking at the multiple sample variations by way of ANOVA