# colpoisdisp.tests: Many tests for the dispersion parameter in Poisson... In Rfast: A Collection of Efficient and Extremely Fast R Functions

## Description

Many tests for the dispersion parameter in Poisson distribution.

## Usage

 ```1 2``` ```colpoisdisp.tests(y, alternative = "either", logged = FALSE) colpois.tests(y, logged = FALSE) ```

## Arguments

 `y` A numerical matrix with count data, 0, 1,... `alternative` Do you want to test specifically for either over or underspirsion ("either"), overdispersion ("over") or undersispersion ("under")? `logged` Set to TRUE if you want the logarithm of the p-value.

## Value

A matrix with two columns, the test statistic and the (logged) p-value.

Michail Tsagris

## References

Yang Zhao, James W. Hardin, and Cheryl L. Addy. (2009). A score test for overdispersion in Poisson regression based on the generalized Poisson-2 model. Journal of statistical planning and inference 139(4):1514-1521.

Dimitris Karlis and Evdokia Xekalaki (2000). A Simulation Comparison of Several Procedures for Testing the Poisson Assumption. Journal of the Royal Statistical Society. Series D (The Statistician), 49(3): 355-382.

Bohning, D., Dietz, E., Schaub, R., Schlattmann, P. and Lindsay, B. (1994) The distribution of the likelihood ratio for mixtures of densities from the one-parameter exponential family. Annals of the Institute of Statistical Mathematics, 46(): 373-388.

``` poisson.mle, negbin.mle, poisson.anova, poisson.anovas, poisson_only ```
 ```1 2 3 4 5 6 7 8``` ```y <- matrix(rnbinom(100* 50, 10, 0.6), ncol = 50) a1 <- colpoisdisp.tests(y, "over") b1 <- colpois.tests(y) y <- matrix(rpois(100* 50, 10), ncol = 50) a2 <- colpoisdisp.tests(y, "either") b2 <- colpois.tests(y) y <- NULL ```