# bc.ppm

##### Bias Correction for Fitted Model

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

##### Usage

`bc(fit, …)` # S3 method for 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.

##### 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

##### Examples

```
# NOT RUN {
fit <- ppm(cells ~ x, Strauss(0.07))
coef(fit)
if(!interactive()) {
bc(fit, nfine=64)
} else {
bc(fit)
}
# }
```

*Documentation reproduced from package spatstat, version 1.63-0, License: GPL (>= 2)*