The best way to do this is with a comprehensive micro-analytical simulation model that includes all aspects of individual income, consumption, taxes and transfers. However, this requires an excellent database at the level of households and individuals (preferably in the form of panel data).
That is a good question. I see two answers. The first is if you can get unbiased, fact-based, up-to-date data. The second is if the person who wants to do the study can work with those who are in need, such as the poor, the unemployed, and the marginalized. The second is much better than the first.