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October 6th, 2010

Tactical voting will still occur under the Alternative Vote, but much less so than under First Past the Post

8 comments

Estimated reading time: 5 minutes

Blog Admin

October 6th, 2010

Tactical voting will still occur under the Alternative Vote, but much less so than under First Past the Post

8 comments

Estimated reading time: 5 minutes

Exactly what will change if the UK adopts the Alternative Vote (AV) system in next May’s referendum? Reformers argue that AV removes any need for large numbers of voters to choose to vote tactically, rather than supporting their top preference party. But social science theory insists that tactical voting can occur under all voting systems, although showing up in different ways. Rafael Hortala-Vallve makes clear that AV will probably cut the incidence of tactical voting, but cannot get rid of it altogether.

Tactical voting denotes any situation where voters can improve their welfare (get a better outcome, given their preferences) by supporting a party that is not their top preference, that is by voting ‘insincerely’ for a party that is lower down their preference ranking but has more chance of winning, or defeating a strongly disliked opposing party. Under first past the post elections at present, of course, many voters are forced to vote tactically so as to avoid their votes being ‘wasted’.

This blog has seen a lively debate on whether tactical voting would continue if Britain votes to adopt the Australian system of Alternative Vote in the May 2011 referendum – see comments on earlier posts by Roger Mortimore, Andy White, and myself. Luckily, there is no disagreement amongst us that tactical voting remains a theoretical possibility under AV. Instead the disagreement focuses on whether tactical voting is at all likely in future UK elections held under AV. With the following example I’ll show that tactical voting may indeed be less likely under AV than under FPTP, but it is still a very likely event.

Before doing so I want to make sure we all agree on what is tactical voting (also called strategic voting, rather confusingly). A player (in the game-theory sense) acts strategically when he acts to maximize his own utility, while taking into account all other players’ actions. In a voting situation being strategic implies (1) taking into account the expected votes of other citizens, and (2) voting for the party  that maximises expected utility (i.e. utility times the probability that the individual’s vote is pivotal). Note that often (indeed usually) a strategic vote may also coincide with supporting the party that is most preferred by the player. However, a sincere voter will stick with voting their top preference even if this produces a poorer result for them. In this post I will say that a voter is tactical when s/he is strategic and s/he is not voting her/his top preference.

First Past the Post

A typical constituency that displays tactical voting under FPTP is one where there is a progressive majority but the Conservatives have plurality support. (Alternatively, we could think of a constituency with a conservative majority but with plurality support towards a progressive party).

As an example think of the following preferences in the population:

35% Labour, 25% Liberal Democrats and 40% Tories.

In some circumstances we may observe the supporters of one of the progressive parties voting tactically in order to avoid a Tory candidate. In the previous example, some Liberal Democrat supporters may vote for the Labour candidate to ensure that the Tories do not win. In a way, the tactical vote does what the voting rule cannot do: it allows a majority of citizens to select a candidate that is preferred by them.

Alternative Vote

Let’s now analyse what would happen under AV. Some at least of the Tory supporters know that, once second preferences are taken into account, it is impossible for them to win (because there is a progressive majority in the constituency). However, they can try to influence which progressive candidate is elected. They especially want to do so when the progressive candidate that has most support among progressive citizens is the one they most dislike.

Suppose then that the second and third preferences in the previous example are set up in the following highly simplified way:

35% of voters prefer Labour to LibDem, and then LibDem to Tory

25% prefer LibDem to Labour, and then Labour to Tory

40% prefer Tory to LibDem, and then LibDem to Labour

In the above example, under the Alternative Vote sincere voting by everyone will elect a Labour candidate.  However, some of the Tory voters could act strategically by marking the Liberal Democrat candidate as their first preference, and the Conservatives second. If 11 per cent of voters follow this course of action, the Tory candidate is eliminated under AV, the Liberal Democrat candidate is elected in a run-off against Labour. Notice here that the tactical vote of relatively few citizens (11 per cent) makes a majority (65 per cent) of all citizens better off than if everyone votes sincerely!

On strategic voting

So tactical voting is indeed a possibility under both electoral rules. However, the citizens that act tactically are not the same. In my example, under FPTP the Liberal Democrat supporters vote tactically, but under AV some of the Tory voters vote tactically. When there is a progressive majority but a conservative party has plurality support, then there is always scope for tactical voting under FPTP. The same thing applies in reverse if there is a locally conservative majority of Tory and Liberal Democrat supporters (as there may be under the current coalition government) but Labour has the largest single vote, hence the intense discussion of electoral pacts at the recent Tory conference fringe. Under AV, however, there will only be tactical voting when supporters of the party with plurality support prefers a centrist candidate that would not be elected unless the run-off stage is altered to include them.

It follows that tactical voting is less likely to occur under AV. In addition, social science research has also shown that voters are less likely to act strategically with voting rules that are more complex. Now  AV is slightly more complicated than FPTP, and so recent work shows that we should expect less tactical voting here. However, there is also evidence of a different kind that the amount of tactical voting in proportional representation (PR) systems and FPTP systems is surprisingly similar. This effect occurs because the number of parties is mostly higher in PR systems  (i.e. it is endogenous to the vote counting process being used). With more small parties in PR systems, the opportunities for voters to behave tactically increase (see Abramson et al, 2010). The number of parties in Britain is likely to rise somewhat under AV, so this will offset the effects above.

Notice also that tactical voting under AV may not only be observed by manipulating preference transfers or second preferences, which requires a high level of precision in knowing citizens’ preferences (as recent posts on this blog by Roger Mortimore or Andy White) have argued. It may instead be observed by directly manipulating the person that gets first preferences. Tactical voting of this second kind only requires the sort of information that is needed under FPTP.

Finally, I’d like to emphasise that tactical voting may not be that bad a thing. In my example above, tactical voting has allowed the selection of  a candidate that is preferred by a majority of citizens. It would be difficult to disagree with the wish of finding electoral rules that are not manipulable -such manipulations do usually benefit those who are better at computing the best strategy or those who have better information. In most circumstances it allows voters to achieve overcome the limitations of the voting rule and achieve an outcome that is better for them.

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Posted In: Alternative Vote (AV) referendum | Electoral and constitutional reform

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