anova.ppm

0th

Percentile

ANOVA for Fitted Point Process Models

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

Keywords
models, methods, spatial
Usage
## S3 method for class 'ppm':
anova(object, \dots, test=NULL, adjust=TRUE, warn=TRUE)
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", "LRT", "Rao" or "score".
adjust
Logical value indicating whether to correct the pseudolikelihood ratio when some of the models are not Poisson processes.
warn
Logical value indicating whether to issue warnings if problems arise.
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 by default, 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" or test="LRT") the two-sided p-values for the chi-squared tests. Their interpretation is very similar to that in anova.glm. If test="Rao" or test="score", the score test (Rao, 1948) is performed instead.

If some of the fitted models are not Poisson point processes, the `deviance' differences in this table are 'pseudo-deviances' equal to 2 times the differences in the maximised values of the log pseudolikelihood (see ppm). It is not valid to compare these values to the chi-squared distribution. In this case, if adjust=TRUE (the default), the pseudo-deviances will be adjusted using the method of Pace et al (2011) so that the chi-squared test is valid. It is strongly advisable to perform this adjustment.

Value

  • An object of class "anova", or NULL.

References

Baddeley, A., Turner, R. and Rubak, E. (2014) Adjusted composite likelihood ratio test for Gibbs point processes. Submitted for publication.

Pace, L., Salvan, A. and Sartori, N. (2011) Adjusting composite likelihood ratio statistics. Statistica Sinica 21, 129--148.

Rao, C.R. (1948) Large sample tests of statistical hypotheses concerning several parameters with applications to problems of estimation. Proceedings of the Cambridge Philosophical Society 44, 50--57.

See Also

ppm

Aliases
  • anova.ppm
Examples
mod0 <- ppm(swedishpines ~1)
 modx <- ppm(swedishpines ~x)
 anova(mod0, modx, test="Chi")
 anova(mod0, modx, test="Rao")

 modxy <- ppm(swedishpines ~x + y)
 anova(modxy, test="Chi")

 modP <- ppm(swedishpines ~1, rbord=9)
 modS <- ppm(swedishpines ~1, Strauss(9))
 anova(modP, modS, test="Chi")
Documentation reproduced from package spatstat, version 1.42-2, License: GPL (>= 2)

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