Given a random variable defined over , and given that is normally distributed with mean and standard deviation , the random variable follows the Lognormal distribution, defined by the probability density function. The probability density function is The lognormal distribution function is where and . The mean and standard deviation of the random variable are given as follows: and The lognormal probability density function, as shown in the figure below,
is often used to describe material properties, sizes from a breakage
process, and the life of some types of transistors. |