The calculation of the tax rate may vary depending on whether the taxpayer is resident in the country.
The determination of the State in which the taxpayer is resident is dependent on an assessment of the criteria set out in the double taxation treaty between the specific countries to be considered for that taxpayer.
Most countries in the world have are obligated by double taxation treaties. Double taxation treaties may vary in detail, such as taxation of shipping or airline staff, student exemption, taxation of a US citizen (former citizen as well).
It is easy to determine the residence if the taxpayer lives the whole year with the family, or even by himself (if he does not have a close family depending on him). The taxpayer is a resident of a country if he has a permanent home and is employed throughout the year in that country.
Alternatively, if the taxpayer moves with his family to another country during the year (meaning they no longer have a permanent residence or an economic interest in the original country) they are still considered as residents for the rest of the corresponding tax year.
In other cases, it is more difficult to determine residence status and we recommend consulting with tax advisor.