standard deviation
  • noun a measure of the amount by which a set of values differs from the arithmetic mean
  • A statistical measure of the dispersion or spread around the mean, for a given set, series, or population. It is equal to the square root of the variance. If a data set has as a bell-shaped distribution, for instance, 68.3% of the data will fall on either side of one standard deviation, 95.5% within two standard deviation, 99.7% within three, and so on. Its abbreviation is SD. Its symbol is σ.

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