Wikipedia 10K Redux by Reagle from Starling archive. Bugs abound!!!

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back to [[Summarizing Statistical Data]] -- [[Probability Distributions]]

The Cumulative Distribution Function (abbreviated '''cdf''') describes the probability distribution of a quantitative [[Random Variable]], X, completely. For every possible value, x, in the range, the cdf is given by

:F(x) = Pr[X<=x], 

that is the probability that X is no greater than x.

If X is a [[Discrete Random Variable]], then the probability is concentrated on discrete points and F(x) can be described as a sequence of pairs  where p(x) = Pr[X=x].

If X is a [[Continuous Random Variable]], the the [[Probability Density]], f(x), is distributed over an interval (or collection of intervals) and can be described as the derivative of F(x) with respect to x.
[[Dick Beldin]]