The Lincoln-Petersen Method for Estimating Population Size
Various methods exist for estimating population size, each involving a different set of assumptions and a different statistical method for calculating the estimated population size. One of the simplest methods is the Lincoln-Petersen Method. It assumes the following:

1) The population is sampled only twice. Once initially to mark a subset and again later to count the number of recaptures.

2) The population must be closed during the sampling period.

3) Each individaul in the population has an equal probability of being captured.

4) The mark used to identify the individual does not harm the animal or reduce the likelyhood of its being captured again in the second session.

The data required are:

n1 = number of marked and released individuals in the first session.

n2 = total number captured in the second session.

m2 = number found marked in the second session.

The total population size (N) is calculated as:

The applet below calculates N based on the user input data.
The applet will also calculate the 95% confidence intervals for N based on the formula below:

p = m2/n2

Calculate the plus and minus values W1 and W2:

To obtain the 95% confidence values for N, divide W1 and W2 into n1.
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