A method for estimating the size of a population. The method is generally applied to living organisms, such as fish in a lake.
The simplest example proceeds as follows. A sample of n1 individuals is obtained from the population (for example, by catching fish in a net). Each of these individuals is now marked in some fashion (for example, by attaching a tag) and is returned to the population. Later, a second sample (of n2 individuals) is taken from the population. Suppose m of these individuals are tagged. The sample proportion of tagged individuals is m/n2, and the population proportion is n1/N, so that an estimate of the population size, N, is N̂, given by . This estimate is known as the Petersen estimator of the population size. An alternative that avoids the problem caused when m is zero is provided by the Chapman estimator:.
Subjects: Probability and Statistics.