theta.mm {MASS} | R Documentation

## Estimate theta of the Negative Binomial by Moments

### Description

Given the mean estimate, calculate the moment estimator of theta by equating `sum((y-mu)^2/(mu+mu^2/theta))` to the residual degrees of freedom.

### Usage

    theta.mm(y, u, dfr, limit=10, eps=.Machine$double.eps^0.25)

### Arguments

`y` | Vector of observed values from the Negative Binomial.
`u` | Estimated mean vector.
`dfr` | Residual degrees of freedom (assuming `theta` known).
`limit` | Limit on the number of iterations.
`eps` | Tolerance to determine convergence.

### Value

The required estimate of `theta`, as a scalar.

### See Also

`glm.nb`, `theta.ml`, `theta.md`

### Examples

    theta <- theta.mm(y, fitted(fm), dfr=123)