rChapman {recapr}

Random Draws from the Chapman Estimator

Description

Returns a vector of random draws from the Chapman estimator in a mark-recapture experiment, given values of the true abundance and the sample size in both events. The function first simulates a vector of recaptures (m2) from a hypergeometric distribution, and then uses these to compute a vector of draws from the estimator.

If capture probabilities (p1 and/or p2) are specified instead of sample size(s), the sample size(s) will first be drawn from a binomial distribution, then the number of recaptures. If both sample size and capture probability are specified for a given sampling event, only the sample size will be used.

Usage

rChapman(length, N, n1 = NULL, n2 = NULL, p1 = NULL, p2 = NULL)

Arguments

length

The length of the random vector to return.

N

The value of the true abundance. This may be a single number or vector of values equal to length.

n1

Number of individuals captured and marked in the first sample. This may be a single number or vector of values equal to length.

n2

Number of individuals captured in the second sample. This may be a single number or vector of values equal to length.

p1

Alternately, probability of capture in the first sample. This may be a single number or vector of values equal to length.

p2

Alternately, probability of capture in the second sample. This may be a single number or vector of values equal to length.

Value

A vector of random draws from the Chapman estimator

Note

Any Petersen-type estimator (such as this) depends on a set of assumptions:

• The population is closed; that is, that there are no births, deaths, immigration, or emigration between sampling events

• All individuals have the same probability of capture in one of the two events, or complete mixing occurs between events

• Marking in the first event does not affect probability of recapture in the second event

• Individuals do not lose marks between events

• All marks will be reported in the second event

Author(s)

Matt Tyers

See Also

NChapman, vChapman, seChapman, pChapman, powChapman, ciChapman

Examples

draws <- rChapman(length=100000, N=500, n1=100, n2=100)
plotdiscdensity(draws)  #plots the density of a vector of discrete values