# theta.k: Population Parameter THETA using Expected Number of Alleles In pegas: Population and Evolutionary Genetics Analysis System

## Description

This function computes the population parameter THETA using the expected number of alleles.

## Usage

 `1` ```theta.k(x, n = NULL, k = NULL) ```

## Arguments

 `x` a vector or a factor. `n` a numeric giving the sample size. `k` a numeric giving the number of alleles.

## Details

This function can be used in two ways: either with a vector giving the individual genotypes from which the sample size and number of alleles are derived (e.g., `theta.k(x)`), or giving directly these two quantities (e.g., `theta.k(n = 50, k = 5)`).

The argument `x` can be either a factor or a vector. If it is a factor, then it is taken to give the individual alleles in the population. If it is a numeric vector, then its values are taken to be the numbers of each allele in the population. If it is a non-numeric vector, it is a coerced as a factor.

Both arguments `n` and `k` must be single numeric values.

## Value

A numeric vector of length one with the estimated theta.

## Note

For the moment, no standard-error or confidence interval is computed.

## References

Ewens, W. J. (1972) The sampling theory of selectively neutral alleles. Theoretical Population Biology, 3, 87–112.

`theta.h`, `theta.s`, `theta.tree`
 ```1 2 3 4 5``` ```data(jaguar) ## compute frequencies: S <- summary(jaguar) ## compute THETA for all loci: sapply(S, function(x) theta.k(x\$allele)) ```