To prevent exhausted ballots, some PR-STV systems instead oblige voters to give a complete ordering of all of the candidates in an election (if a voter does not rank all candidates their ballot may be considered spoilt). However, when there is a large number of candidates that requirement may prove burdensome and can lead to random voting, or "donkey voting" in which a voter that has no strong opinions about their lower preferences simply chooses them in the given order. Some jurisdictions compromise by setting a minimum number of preferences that must be filled for a ballot paper to be valid (for example Tasmania, which requires five preferences).