# anova.ppm

##### ANOVA for Fitted Point Process Models

Performs analysis of deviance for two or more fitted point process models.

##### Usage

```
## S3 method for class 'ppm':
anova(object, \dots, test=NULL, override=FALSE)
```

##### Arguments

- object
- A fitted point process model
(object of class
`"ppm"`

). - ...
- One or more fitted point process models.
- test
- Character string, partially matching one of
`"Chisq"`

,`"F"`

or`"Cp"`

. - override
- Logical flag indicating whether to proceed even when there is no statistical theory to support the calculation.

##### Details

This is a method for `anova`

for
fitted point process models (objects of class `"ppm"`

,
usually generated by the model-fitting function `ppm`

).

If the fitted models are all Poisson point processes,
then this function performs an Analysis of Deviance of
the fitted models. The output shows the deviance differences
(i.e. 2 times log likelihood ratio),
the difference in degrees of freedom, and (if `test="Chi"`

)
the two-sided p-values for the chi-squared tests. Their interpretation
is very similar to that in `anova.glm`

.

If some of the fitted models are *not* Poisson point processes,
then there is no statistical theory available to support
a similar analysis. The function issues a warning,
and (by default) returns a `NULL`

value.

However if `override=TRUE`

,
then a kind of analysis of deviance table will be printed.
The `deviance' differences in this table are equal to 2 times the differences
in the maximised values of the log pseudolikelihood (see
`ppm`

). At the time of writing, there is no statistical
theory to support inferential interpretation of log pseudolikelihood
ratios. The `override`

option is provided for research purposes
only!

##### Value

- An object of class
`"anova"`

, or`NULL`

.

##### See Also

##### Examples

```
data(swedishpines)
mod0 <- ppm(swedishpines, ~1, Poisson())
modx <- ppm(swedishpines, ~x, Poisson())
anova.ppm(modx, mod0, test="Chi")
```

*Documentation reproduced from package spatstat, version 1.9-3, License: GPL version 2 or newer*