The outcome of most votes can be predicted beforehand since political parties normally instruct members which way to vote. Parties entrust some MSPs, known as whips, with the task of ensuring that party members vote according to the party line. MSPs do not tend to vote against such instructions, since those who do are unlikely to reach higher political ranks in their parties. Errant members can be deselected as official party candidates during future elections, and, in serious cases, may be expelled from their parties outright. Thus, as with many Parliaments, the independence of Members of the Scottish Parliament tends to be low, and backbench rebellions by members who are discontent with their party's policies are rare. In some circumstances, however, parties announce "free votes", which allows Members to vote as they please. This is typically done on moral issues.