Gamma Distribution

The gamma distribution models the total time to finish several independent steps, giving a positive, right-skewed value. It is a general form that includes the exponential and the Erlang as special cases.

Write Gamma(shape, rate):

Gamma(2, 0.5)

The shape sets how many stages worth of time is being added up and the rate sets how quickly each is completed. Use it for a positive duration that is skewed toward shorter times with a long tail, where a symmetric normal would not fit.