Citizens abroad on Election Day may be roughly divided into three categories: those permanently abroad, who may be double nationals; those staying temporarily abroad (for example for academic or employment purposes); and those who are just travelling abroad on Election Day (for business or personal reasons). The population registers and/or on the electoral lists – which are often derived from the latter – include of course the third category, but they include a number of citizens belonging to the second and even the first category (emigrants) too. The more or less high level of emigrants still on the in-country register may depend on a number of factors, such as the definition of residence by national law, incentives or disincentives to remain registered (such as social benefits on the one side and fiscal or military obligations on the other side), pro-activeness or inertia of the administration, or a legal obligation for all citizens to declare a residence in-country.