In statistics, a function that can take on either a finite number of values, each with an associated probability, or an infinite number of values, whose probabilities are summarized by a density function. Used in studying chance events, it is defined so as to account for all possible outcomes of the event. When these are finite (e.g., the number of heads in a three-coin toss), the random variable is called discrete and the probabilities of the outcomes sum to 1. If the possible outcomes are infinite (e.g., the life expectancy of a light bulb), the random variable is called continuous and corresponds to a density function whose integral over the entire range of outcomes equals 1. Probabilities for specific outcomes are determined by summing probabilities (in the discrete case) or by integrating the density function over an interval corresponding to that outcome (in the continuous case).
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