ABSTRACT
Ordinal response data are often encountered in biological studies. For example, in a field survey data for the Invasive Plant Atlas of New England (IPANE), the abundance of Berberis thunbergiis is classified into 6 categories, with the higher number indicating higher coverage. In this particular data, Berberis thunbergiis does not exist in many locations, therefore creating extremely unbalanced data. Figure 16.1 shows the collection sites of the IPANE data across New England. Standard link functions such as logit and cloglog may not work well in this situation and a flexible link function may be needed.
