Variance

variance

A measure of variability (or spread).

It is denoted by σ² and defined as the mean-square deviation from the mean, that is, the mean of the squares of the differences between individual values of x and the mean value μ:

where E denotes expected value. The positive square root σ of the variance is called the standard deviation. An unbiased estimate s² of the variance σ² is obtained from n independent observations x₁, x₂, · · ·, x_n and their sample average

as follows:

and the positive square root s of s² is taken as an estimate of the standard deviation σ.

INDEX
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q
R
S
T
U
V
W
X
Y
Z
0
1
2
3
4
5
6
7
8
9