 If "X" is a random variable with a Pareto (Type I) distribution, then the probability that "X" is greater than some number "x", i.e.the survival function (also called tail function), is given by

where "x"m is the (necessarily positive) minimum possible value of "X", and "α" is a positive parameter.The Pareto Type I distribution is characterized by a scale parameter "x"m and a shape parameter "α", which is known as the "tail index".