The log-normal distribution
The log-normal distribution is simply the distribution of a set of values whose logarithm is normally distributed. The base of the logarithm can be any positive number except for one. Like the normal distribution, the log-normal distribution is important in the description of many naturally occurring phenomena.
A logarithm represents the power to which a fixed number (the base) must be raised to produce a given number. By plotting the logarithms as a histogram, we've shown that these powers are approximately normally distributed. Logarithms are usually taken to base 10 or base e: the transcendental number that's equal to approximately 2.718. Incanter's log function and its inverse exp both use base e. loge is also called the natural logarithm or ln, because of the properties that make it particularly suitable in calculus.
The log-normal distribution tends to occur in processes of growth where the growth rate is independent of size. This is known as Gibrat's law...
