Chebyshev's inequality - Wikipedia
https://en.wikipedia.org/wiki/Chebyshev's_inequalityIn probability theory, Chebyshev's inequality (also called the Bienaymé–Chebyshev inequality) guarantees that, for a wide class of probability distributions, no more than a certain fraction of values can be more than a certain distance from the mean. Specifically, no more than 1/k of the distribution's values can be k or more standard deviationsaway from the mean (or equivalently, over 1 − 1/k of the distribution's values are less than k standard deviations away from the mean)…
Chebyshev's Theorem
mathcenter.oxford.emory.edu › site › math117This relationship is described by Chebyshev's Theorem: For every population of n values and real value k > 1, the proportion of values within k standard deviations of the mean is at least. 1 − 1 k 2. As an example, for any data set, at least 75% of the data will like in the interval ( x ¯ − 2 s, x ¯ + 2 s). To see why this is true, suppose a population of n values consists of n 1 values of x 1, n 2 values of x 2, etc. (i.e., n i values of each different x i in the population).