Design for Six Sigma for Green Belts and Champions: Applications for Service Operations—Foundations, Tools, DMADV, Cases, and Certification

Appendix A. Summation Notation

Because the operation of addition occurs so frequently in statistics, the special symbol Σ is used to mean “take the sum of.” If there is a set of n values for a variable labeled X, the expression means that these n values are to be added together from the first value to the last (n^th) value. Thus,

To illustrate summation notation, suppose there are five values for a variable X:

X₁ = 2, X₂ = 0, X₃ = -1, X₄ = 5, and X₅ = 7

For these data,

In statistics, it is also often necessary to sum the squared values of a variable. ...