Deviance and Chi-squared Goodness-of-Fit Test for Poisson Models

Deviance and Chi-squared goodness-of-fit test of the null hypothesis that poisson variance is appropriate to model the conditional dispersion of the data, given a particular model.

poisGOF(obj)

Arguments

obj	A model object of class glm (with family=poisson).

Value

A 2x2 data frame with rows representing the different types of statistics (Deviance and Chi-squared) and columns representing the test statistic and p-value.

References

Dobson, A. J. (1990) An Introduction to Generalized Linear Models. London: Chapman and Hall.

Examples

## Example taken from MASS help file for glm, identified to be
## Dobson (1990) Page 93: Randomized Controlled Trial :
counts <- c(18,17,15,20,10,20,25,13,12)
outcome <- gl(3,1,9)
treatment <- gl(3,3)
print(d.AD <- data.frame(treatment, outcome, counts))
#>   treatment outcome counts
#> 1         1       1     18
#> 2         1       2     17
#> 3         1       3     15
#> 4         2       1     20
#> 5         2       2     10
#> 6         2       3     20
#> 7         3       1     25
#> 8         3       2     13
#> 9         3       3     12
glm.D93 <- glm(counts ~ outcome + treatment, family=poisson())
poisGOF(glm.D93)
#>              Stat p-value
#> Chi-squared 5.173   0.270
#> Deviance    5.129   0.274