Summation Notation
Prerequisites
None
Learning Objectives
 Use summation notation to express the sum of all numbers
 Use summation notation to express the sum of a subset of numbers
 Use summation notation to express the sum of squares
Many statistical formulas involve summing numbers.
Fortunately there is a convenient notation for expressing summation.
This section covers the basics of this summation
notation.
The following formula means to sum up four numbers:
The Greek letter Σ
indicates summation. The "i = 1" at the bottom indicates
that the summation is to start with X1
and the 4 at the top indicates that the summation will end with
X4. The Xi indicates
that X is the variable to be summed as i goes from 1 to 4.
When all the scores of a variable (such as X)
are to be summed, it is often convenient to use the following
abbreviated notation:
Thus when no values of i are shown, it means to
sum all the values of X.
