Statistics and Probability Glossary
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Mean
A mean score is an average score, often denoted by X.
It is the sum of individual scores divided by the number of individuals. Thus,
if you have a set of N numbers (
X1
,
X2
,
X3
, . . .
XN
), the mean of those numbers
would be defined as:
X = (
X1
+
X2
+
X3
+ . . . +
XN
) / N = [ Σ Xi ] / N
For example, the mean of the numbers 1, 2, and 3 would be (1 + 2 + 3)/3 or 2.
Note: The mean score of a random variable (also called the
expected value) is defined somewhat differently. See
expected value.
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