Contingent Vote - Tactical Voting

Tactical Voting

Like virtually all electoral systems (see the Gibbard-Satterthwaite theorem), the contingent vote is open to tactical voting. In particular, like both the two round system and instant-runoff voting, it is vulnerable to the tactics of 'push-over' and 'compromise'. Under the contingent vote compromising occurs where a voter gives a first or other high preference to a candidate not because they necessarily support them, but as a way of avoiding the election of a candidate who they dislike even more. The contingent vote is more vulnerable to compromising than IRV. In the first example given in this article if a large number of Catherine supporters had 'compromised', and given a first preference to Brian, then Brian would have been elected instead of Andrew, a candidate who Catherine supporters dislike even more. This tactic would have been effective under IRV as well as the contingent vote. In Example II Brad supporters, had they predicted that Brad would not make it to the second round, could have compromised by giving their first preferences to Carter, and thereby have ensured his election. This would not have been a necessary tactic under IRV because the votes of Brad supporters would have ended up with Carter anyway—when Brad was eliminated they would have transferred to him.

However the contingent vote is less vulnerable to the tactic of compromise than the 'first-past-the-post' (plurality) system. This is because the contingent vote's system of transferring votes means that even if a voter's first choice is unlikely to be elected, her vote may still have a chance to be transferred to one of her subsequent preferences. In Example I above Catherine would have won under the plurality system because she has more votes than any other candidate. However Brian voters would have been able to ensure the election of their second choice, Andrew, by voting tactically for Andrew instead of Brian, but this contingent (tactical) vote would prevent Brian's electoral support being recorded, thus in a plurality or First-past-the-post voting system 3rd party candidates are either labelled Spoilers or their real support goes unrecognised. Contingent voting is not necessary under IRV because (in this exampe) Brian's votes will transfer to Andrew in the second round anyway.

'Push-over' is a tactic by which a voter insincerely ranks an unpopular 'push-over' candidate higher than her real first choice. The purpose of voting for the 'push-over' is to ensure that it is this weak candidate, rather than a more popular rival, who remains to challenge her preferred candidate in the second round. By supporting a push-over candidate it is hoped to eliminate a stronger candidate who might have gone on to win the election. Under the contingent vote a voter uses the tactic by giving her first preference to a 'push over' and her lower preferences to the candidates she really supports.

The push-over tactic requires voters to be able to reliably predict how others will vote. It runs the risk of backfiring, because if the tactical voter miscalculates then the candidate intended as a push-over might end up actually beating the voter's preferred candidate. It also requires voters to understand the tactic and be aware that it exists. For these reasons some doubt that push-over is likely to be a factor in real elections. Because under the contingent vote, as under IRV, it is paradoxically possible to harm the chances of a candidate by giving them a first preference, or to aid the chances of a candidate by ranking them lower than first, the system is said to fail the monotonicity criterion.