Practical Computing Exercise for Week 7: Snails

Download the template R markdown file for this workshop.

Aims of this practical exercise

In this exercise you will:

  • fit binomial and quasibinomial based models
  • compare the impact of going “quasi”

The MASS package includes a dataset detailing the death of snails under experimental conditions. Obtain it using:

data(snails, package="MASS")
str(snails)

  1. Convert the relevant variables into factors.

  2. Choose a sensible model for the data. N.B. Under most experiments, we fit a model that includes all interactions of factors.

  3. What happens if you alter the family to quasibinomial?

  4. Let’s remove a significant factor from this model so that we can see how this impacts on our findings above. Fit both binomial and `quasibinomial versions, and compare.

Solutions

You should compare your work with the solutions for this workshop.