Extending ordinal regression with a latent zero-augmented beta distribution

Journal of Agricultural, Biological, and Environmental Statistics
By: , and 

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Abstract

Ecological abundance data are often recorded on an ordinal scale in which the lowest category represents species absence. One common example is when plant species cover is visually assessedwithin bounded quadrats and then assigned to pre-defined cover class categories.We present an ordinal beta hurdle model that directly models ordinal category probabilitieswith a biologically realistic beta-distributed latent variable.Ahurdle-at-zero model allows ecologists to explore distribution (absence) and abundance processes in an integrated framework. This provides an alternative to cumulative link models when data are inconsistent with the assumption that the odds ofmoving into a higher category are the same for all categories (proportional odds). Graphical tools and a deviance information criterion were developed to assess whether a hurdle-at-zero model should be used for inferences rather than standard ordinal methods. Hurdle-at-zero and non-hurdle ordinal models fit to vegetation cover class data produced substantially different conclusions.The ordinal beta hurdle model yielded more precise parameter estimates than cumulative logit models, although out-of-sample predictions were similar. The ordinal beta hurdle model provides inferences directly on the latent biological variable of interest, percent cover, and supports exploration of more realistic ecological patterns and processes through the hurdle-at-zero or two-part specification.We provide JAGS code as an on-line supplement. Supplementary materials accompanying this paper appear on-line.
Publication type Article
Publication Subtype Journal Article
Title Extending ordinal regression with a latent zero-augmented beta distribution
Series title Journal of Agricultural, Biological, and Environmental Statistics
DOI 10.1007/s13253-016-0265-2
Volume 21
Issue 4
Year Published 2016
Language English
Publisher Springer
Contributing office(s) Northern Rocky Mountain Science Center
Description 22 p.
First page 619
Last page 640
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