Statistics for Maintenance Modelling: Continuous Lifetime Distributions 2

# The Cumulative and Reliability Functions for the Gamma Distribution¤

The gamma distribution gives rise to curves similar to those of the Weibull distribution. However the gamma distribution leads to more complicated equations, e.g. for the reliability/survival function.

There is no simple analytical form for the cumulative distribution function - the simplest form involves an infinite series of ratios of gamma functions. Fortunately Excel provides functions for calculating the probability density function and the cumulative distribution function, as well as the inverse of the cumulative distribution function.

Click here to find out how to calculate the Gamma distribution in Excel.

The shape of the reliability function is shown on the right: