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单词 hypergeometric distribution
释义
hypergeometric distribution

Mathematics
  • Suppose that, in a set of N items, M items have a certain property and the remainder do not. A sample of n items is taken from the set. The discrete probability distribution for the number r of items in the sample having the property has probability mass function given by Pr(X=r)=MCrN-MCnrNCn where r runs from 0 up to the smaller of M and n. This is called a hypergeometric distribution. The mean is nMN, and the variance is

    nM(NM)(Nn)N2(N1).


Statistics
  • The distribution of the number of ‘successes’ when sampling without replacement from a finite population each of whose members is classified as either a ‘success’ or a ‘failure’. As an example, suppose that an urn contains N balls of which w are white. Suppose n balls are taken from the urn at random and without replacement, and let the random variable X be the number of white balls obtained. Then X has the hypergeometric distribution given by hypergeometric distributionThe initial derivation of the distribution was published by de Moivre in 1711. The mean of the distribution is nw/N and the variance is hypergeometric distributionFor large values of N the hypergeometric distribution may be approximated by the binomial distribution B(n, p), where p = w/N, since in this case sampling without replacement is approximately equivalent to sampling with replacement.


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