Summation Notation (2 of 4)
In order to make formulas more general, variables can be
used with the summation notation. For example,
means to sum up values of X from 1 to N where N can be any number but
usually indicates the sample size.
Often an abbreviated form of the summation notation is used. For example,
ΣX means to sum all the values of X. When only
a subset of the values of X are to be summed then the full version is
required. Thus, the sum of all elements of X except the first and the
last (the N'th) would be indicated as:
which would be read as
the sum of X with i going from 2 to N-1.
Some formulas require that each number be squared before the numbers
are summed. This is indicated by:
and is equal to 7² + 6² + 5² + 8²