Hutcheon et al. (2002) examined variations in total brain volume and in the volume of three brain regions (main olfactory bulb, hippocampus, auditory nuclei) using a data set for 63 species of bats (Chiroptera). They were primarily interested in determining if the volume of the brain region differed among broad foraging categories (phytophagous, gleaner, and aerial insectivore). A fourth foraging type – vampire bats – was excluded from the analysis. They “factored out” body weight of the bats (by including it as a covariate in their model) because differences in size of bats among the foraging categories was suspected and thought to possibly mask possible differences in the volume of the brain regions. Use the data in Batmorph2.csv (download, meta) to compute results to address the questions below assuming that interest is in just auditory nuclei mass. [Note: You should exclude the vampire bat feeding category as well. You MUST do this within your R code, not by manipulating the CSV file.]
- Construct (i.e., write) the ultimate full model for an indicator variable regression with these data. Use appropriate codes so that the phytophagous foraging group will be considered the reference group. [Note: Clearly define your variables.]
- Construct all possible submodels from your ultimate full model.
- Address all assumptions for the ultimate model. If the major assumptions are not met, then transform the data to a scale where the assumptions are met (and show that the assumptions are met on this new scale). Do not remove any individuals from the analysis.
- Perform a parallel lines test. If the lines are not parallel, then determine which pairs of lines differ.
- If appropriate, perform an intercepts test. If the lines have different intercepts, then determine which pairs of lines are different.
- Write an overall conclusion about the bats from your results.