In practice, preferential votes do not always influence the distribution of mandates within lists. Although the electors can indicate their preferences, a number of conditions have to be fulfilled almost systematically before they can be taken into account. In Belgium, for example, in the case of both Chambers, the votes of electors who have not cast a preferential vote are automatically considered to be preferential votes in favour of the candidates at the top of the lists. Once a sufficient number of votes has been obtained in order to declare the candidate at the head of the list elected, non-preferential votes are counted as being votes in favour of the candidate in second place and so on. For the election of the Austrian National Council, there is a threshold for taking preferential votes into account. The threshold is fixed at a level equivalent to the number of voters in the basic constituency divided by the number of seats to be filled. This generally results in a de facto closed list situation.