package data shouldn't really be multiple objects in a single RData but as a list

[n8thangreen]

should have Vaccine$eff, Vaccine$cost etc

Issue with changing is that this is the legacy use and in the new version of the BCEA book

[n8thangreen]

the right extension for packages should be .rda
we should also have LazyData: true in DESCRIPTION but this creates a warning because Smoking and Vaccine both have eff, cost and treat.
This basically mean we have to do the name of data object as NULL and attach an @alias
This is not the recommended way of doing this and is all a result of us not putting the data in a single list.