Variance 11
Variance 11 :
A measure of variability (or spread). It is denoted by cr2 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 /i. a2 = E[(x - v)2}. = Eix2) - v1 where E denotes expected value. The positive square root o~of the variance is called the standard deviation. An unbiased estimate s2 of the variance o2 is obtained from n independent observations xx, x2, . . . jcn and their sample x average as follows: s2=ii (x,-x)2K-D and the positive square root 5 of s2 is taken as an estimate of the standard deviation a. N.B. Refer to source to verify equation(s)
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