Analysing the relationship between ectomycorrhizal infection and forest decline using marginal models

This statistical survey originates from the problem of discovering
which relationship exists between root ectomycorrhizal infection
and health status of forest plants. The sampling scheme takes
observations from roots that come from sectors around the tree
resulting in a hierarchical association structure of the
observations. Marginal regression models are used to analyze the
mean effect of the ectomycorrhizal state on a response variable
proxy for the health degree of the plants.