Pairing Brown with Blair on a ballot paper might have been unthinkable for the Labour party, yet Michael Marsh, looking at the case of Ireland’s preference voting PR system, illustrates that the choices voters are faced with in the ballot box may play a stronger role in their choice of candidates than either their political knowledge or party loyalty and interest.

Where parties dominate government, and the nominations of candidates for legislative office, the fact that some voters do not appear to structure their electoral choice by one party presents something of a puzzle. US elections are arranged normally so that many offices are filled at the same time, with electors choosing occupants for a range of offices from the grand to the prosaic on a given day. Most voters pick a president and a congressman and more all from the same party, choosing to vote a ‘straight ticket’, but some do not, opting instead for a ‘split ticket’ with perhaps a Republican for President and a Democrat for the Senate. As well as being theoretically problematic, such behaviour may be substantively important as it has consequences for election outcomes. These concepts of ‘straight’ and ‘split’ have travelled beyond the US. Although few countries fill so many offices at the same time, there are features of electoral arrangements elsewhere that offer parallels. The most widely studied are probably mixed member systems, where the voter casts a vote for a party list and another for a representative in a single member district.

Voting in an STV election requires a voter to indicate a first preference for a candidate. In Ireland this simply means placing a ‘1’ next to a candidate’s name. However, voters may continue, expressing further, lower preferences between as many candidates as they wish. In doing so, they are not constrained by the party labels of candidates. Looking at the Irish election of 2011, we can try and find some explanations for split ticket voting.

There are several reasons why this is worthwhile. The first is that STV provides a variant on more widely studied cases and so allows us to further test conventional explanations for their universality. The second, as will be explained below, is that certain types of explanation makes little or no sense in an STV context because of the differences we have already explained. Nonetheless, many alternative explanations are potentially valid. The opportunity to explore some explanations in a context where some alternative ones cannot hold is useful, providing if not a semi-experimental environment, at least one in which many alternatives can be ruled out.

The data used here comes from the Irish election study, which consisted of a post election face–to–face, in–home survey carried out on a sample of 1853 electors in the few weeks after the February 2011 election.

The results show a majority of electors vote a split–ticket, with the number almost identical for each of the three parties who fielded multiple candidates in constituencies.

One source of explanation lies in differences between individuals. Partisanship, and the extent to which voters are attracted by candidates rather than parties are important determinants of straight– and split–ticket behaviour; there is much less evidence that either behaviour is a consequence of the amount of interest, in or information about politics.

A second source, and this appears to be more powerful, lies in what people are asked to do in the ballot box, and in factors connected with the choices they have to make. A voter given just two candidates from his party with names beginning with the same letter, perhaps in a small constituency, and with both being incumbents, is much more likely to vote a straight ticket than the voter faced with three non-incumbents spread out across a long ballot. Parties competing in a mixed member electoral system should then be wary of the subconscious influences that voters can fall prey to and perhaps not focus on the internal politics of appearance on the ballot paper. If a party wants to keep its support intact, on the 2011 evidence it pays to pick a Brown to go with a Blair, and not be tempted to run such candidates in different constituencies or even, separate them on the ballot sheet – despite their internal politics.

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Michael Marsh will be speaking at the next McDougall Trust lunchtime Workshop on Political Representation Issues, Voting Patterns and Public Opinion:  Analysis from the 2011 Irish National Election Study on 19 October. More details.