R: Bias Correction for Fitted Model

bc.ppm {spatstat} | R Documentation

## Bias Correction for Fitted Model

### Description

Applies a first-order bias correction to a fitted model.

### Usage

      bc(fit, ...)

      ## S3 method for class 'ppm'
    bc(fit, ..., nfine = 256)

### Arguments

`fit` | A fitted point process model (object of class `"ppm"`) or a model of some other class.
`...` | Additional arguments are currently ignored.
`nfine` | Grid dimensions for fine grid of locations. An integer, or a pair of integers. See Details.

### Details

This command applies the first order Newton-Raphson bias correction method of Baddeley and Turner (2014, sec 4.2) to a fitted model. The function `bc` is generic, with a method for fitted point process models of class `"ppm"`.

A fine grid of locations, of dimensions `nfine * nfine` or `nfine[2] * nfine[1]`, is created over the original window of the data, and the intensity or conditional intensity of the fitted model is calculated on this grid. The result is used to update the fitted model parameters once by a Newton-Raphson update.

This is only useful if the quadrature points used to fit the original model `fit` are coarser than the grid of points specified by `nfine`.

### Value

A numeric vector, of the same length as `coef(fit)`, giving updated values for the fitted model coefficients.

### Author(s)

Adrian Baddeley Adrian.Baddeley@curtin.edu.au and Rolf Turner r.turner@auckland.ac.nz.

### References

Baddeley, A. and Turner, R. (2014) Bias correction for parameter estimates of spatial point process models. Journal of Statistical Computation and Simulation 84, 1621–1643. DOI: 10.1080/00949655.2012.755976

### See Also

`rex`

### Examples

      fit <- ppm(cells ~ x, Strauss(0.07))
      coef(fit)
      if(!interactive()) {
        bc(fit, nfine=64)
      } else {
        bc(fit)
      }

[Package spatstat version 1.63-3 Index]