# Population growth rate

## Description

In biology or human geography, population growth is the increase in the number of individuals in a population.

The “population growth rate” is the rate at which the number of individuals in a population increases in a given time period, expressed as a fraction of the initial population. Specifically, population growth rate refers to the change in population over a unit time period, often expressed as a percentage of the number of individuals in the population at the beginning of that period. This can be written as the shown formula, valid for a sufficiently small time interval.

## Variables

PGR | Popoulation growth rate (1/yr) |

P(t2) | populaiton at time t2 (dimensionless) |

P(t1) | populaiton at time t1 (dimensionless) |

t_{2} | time when the first sample was taken (P(t2)) (yr) |

t_{1} | time when the first sample was taken (P(t1)) (yr) |