Common Abbreviations Used in Statistical Process Control

GENERAL NOTATION

X	=	A random variable
	=	The ith value of the random variable " x "
	=	Average (bar placed over any variable notation)
ˆ‘	=	"Summation of," add all
^	=	"Estimate of"
'	=	"True value of"
!	=	Symbol for factorial (e.g., n ! is the product of the first n integers times n - 1 times n - 2 times ... times n - n. 0! = 1)

Population	Sample
N	n	Number of items
¼		Average or mean
		Median
ƒ z	S z	Variance
ƒ	S	Standard deviation
R	R	Range