## standard deviation
The sample standard deviation is the positive square root
of the sample variance s^{2},
where variance is defined as the arithmetic
mean of the squares of the deviations of the members of a sample from
the arithmetic mean of the sample. The population standard deviation
σ is given by the square root of the population variance:
where n is the number of observations, μ is the mean,
and x the _{i}ith value. In a normal or Gaussian distribution, about 68.3% of the population lies within one standard deviation of the mean. ## Related category• PROBABILITY AND STATISTICS | |||||||

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