Can someone please explain how the solution to part i) and ii) of this question is worked out? The solution for i) just says 0.2+(0.18-0.12)=0.26 without any explanation of how the formula given for the Additive model has been used to work out the accident frequency. Also, apart from the Brockman & Wright paper recommended in the notes, are there any other papers that explain these 2 models (Additive & Multiplicative) in easy to understand terms with useful worked examples?
So, for an additive model: blue car/blue hair = blue car/red hair plus red car/blue hair minus red car/red hair. Best way to think of it is like using Venn diagrams or Set theory. If you add blue car/red hair people to red car/blue hair people, but then take away all the red car/red hair people, you'll be left with blue car/blue hair people. For more info (probably more than you need), try Duncan Anderson's paper called A Practioner's Guide to Generalized Linear Models: http://www.watsonwyatt.com/europe/news/glmpaper/default.asp
