Data in the accompanying tables and graphs has been sourced from 2 places.
Up to and including the 2015 tax year, a random sample of individual taxpayers was used and scaled up to population estimates. The sample was made up of 10% of IR3 filers and 2% of other taxpayers. It was scaled up to population estimates by weights of 10 for IR3 filers and 50 for other taxpayers.
Population data has also been used from the 2016 tax year onwards.