Definition of a darwin (d):

a change by a factor of *e* per
million years.

Definition of a haldane (h):

a change by a factor of one standard deviation per generation.

- where ln x
_{1}and ln x_{2 }are two sample means of natural logarithms of measurements,- s
_{ln x }is the pooled standard deviation of the ln x_{1}and ln x_{2}values,- delta t is the time difference between the two samples in millions of years, and
- t
_{2 }- t_{1 }is the time difference between the two samples, measured in generations.