<P> All citizens and residents of Denmark are included in the national register, Det Centrale Personregister . Each person is assigned a personal number of ten digits, which include the person's date of birth . The register is used for tax lists, voter lists, membership in the universal health care system, official record of residence, and other purposes . All eligible voters receive a card in the mail before each election which shows the date, time and local polling place; it may only be presented at the designated local polling station . Only citizens may vote in national elections, while long - time residents may vote in local and regional elections . Permanent address within Denmark is required in order to vote . Voting is voluntary . </P> <P> Voter registration in Finland is automatic and based on the national population register . Each citizen is assigned a identification number at birth . Permanent residents are recorded in this register even if they are not citizens, and their citizenship status is indicated in the register . People in the register are legally obliged to notify the register keeper of changes of address . Changing the address in the register automatically notifies all other public bodies (for example the tax district for local taxation, the social security authorities, the conscription authorities) and certain trusted private ones (e.g. banks and insurance companies), making the process of moving residence very simple . Close to election time, the government mails a notification to registered persons informing them of the election and where and when to cast their votes . Only citizens may vote in national elections, but all residents may vote in local elections . </P> <P> All permanent residents of Germany are required to register their place of residence (or the fact that they are homeless) with local government . Citizens who will be 18 or older on the day of voting will automatically receive a notification card in the mail some weeks before any election in which they are eligible to vote: for local elections, resident citizens of other EU countries will also receive these cards and may vote . For European elections, citizens of other EU countries have to register separately . Polling places have lists of all eligible voters resident in the neighborhood served by the particular station; the voter's notification card (or photo ID such as an identity card, passport or driving license, if the notification card is not at hand) is checked against these lists before individuals receive a ballot . Voting is not compulsory . </P> <P> In Hong Kong all permanent residents who are above 18 years of age and do not suffer from a mental illness can register as voters . Imprisoned people can also register and vote since the laws prohibiting them from voting was ruled unconstitutional in 2009 and are able to vote since mid-2010 as the electoral roll is updated annually . The registration process is voluntary . In 2002 around 1.6 million permanent residents did not register . </P>

What is the most important reason for voter registration