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Dictionary definition: standard deviation
- Article from:
- A Dictionary of Weights, Measures, and Units
- Author:
Copyright© A Dictionary of Weights, Measures, and Units 2002, originally published by Oxford University Press 2002. (Hide copyright information)
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standard deviation
statistics. Symbol s.d., σ. A measure of the variability in a set of numbers, equal to the square root of the variance (a less convenient measure of variability, as is also the mean deviation). The deviation for each number is the difference between it and the mean value for the set. Clearly, averaging the signed values would produce zero, by the definition of the mean. The
variance
is the mean of the squares of the deviations, the squaring removing any effect of signs, but compounding the scale factor. The standard deviation is the square root of the variance, bringing the measure back to scale (and prompting its other name of
root-mean-square
; see
r.m.s.
for the ...