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- Title
Dealing with under- and over-dispersed count data in life history, spatial, and community ecology.
- Authors
Lynch, Heather J.; Thorson, James T.; Shelton, Andrew Olaf
- Abstract
Count data arise frequently in ecological analyses, but regularly violate the equi-dispersion constraint imposed by the most popular distribution for analyzing these data, the Poisson distribution. Several approaches for addressing over-dispersion have been developed (e.g., negative binomial distribution), but methods for including both under-dispersion and over-dispersion have been largely overlooked. We provide three specific examples drawn from life-history theory, spatial ecology, and community ecology, and illustrate the use of the Conway-Maxwell-Poisson (CMP) distribution as compared to other common models for count data. We find that where equi-dispersion is violated, the CMP distribution performs significantly better than the Poisson distribution, as assessed by information criteria that account for the CMP's additional distribution parameter. The Conway-Maxwell-Poisson distribution has seen rapid development in other fields such as risk analysis and linguistics, but is relatively unknown in the ecological literature. In addition to providing a more flexible exponential distribution for count data that is easily integrated into generalized linear models, the CMP allows ecologists to focus on the magnitude of under- or over-dispersion as opposed to the simple rejection of the equi-dispersion null hypothesis. By demonstrating its suitability in a variety of common ecological applications, we hope to encourage its wider adoption as a flexible alternative to the Poisson.
- Subjects
ECOLOGICAL research; SPATIAL ecology; DISPERSAL (Ecology); BIOTIC communities; ANIMAL litters; SPECIES diversity; POISSON distribution
- Publication
Ecology, 2014, Vol 95, Issue 11, p3173
- ISSN
0012-9658
- Publication type
Article
- DOI
10.1890/13-1912.1