Modeling multiparty elections , preference classes and strategic voting

We examine the role of strategic motivations in mediating the relationship between underlying political preferences and vote choice, in a multi-party, single member, simple plurality system. Political preference data from the British Election Panel Survey, 19972001, were modeled with mixed multinomial logit models. Latent variables were used to model the stable party political traits underlying observed preferences, allowing correlation between choices and so avoiding the restrictive assumption of independence from irrelevant alternatives. The assumption of normally-distributed latent political traits was found to be violated, so a non-parametric approach was used to specify a discrete distribution of latent classes. In addition to vote data, ranked approval ratings were used to help identify the models and to better characterize the underlying political preferences in the presence of insincere voting, which disproportionately affects ‘third’ parties. From these models we estimate that approximately 9% of votes cast may have been affected by strategic factors. Modeling multiparty elections, preference classes and strategic voting 2 Strategic, non-sincere or tactical voting is widely recognised as being increasingly influential in modern elections, especially in single member plurality systems where there are more than two effective competitors (e.g. Great Britain). However, there is no clear consensus on how strategic voting should be measured, nor on the extent to which subjective notions of strategic voting are consistent with the objective conditions under which such behaviour should (rationally) take place. Blais and Nadeau (1996), and Alvarez and Nagler (2000) identify three approaches to identifying strategic voting based on (i) using aggregate data (e.g. Spafford, 1972; Johnston & Pattie, 1991); (ii) selfreported strategic voting (e.g. Evans and Heath, 1993; Niemi et al, 1993), and; (iii) divergence between stated preferences and vote (e.g. Black, 1978; Blais and Nadeau, 1996). Recognising the potential weaknesses in each of these approaches, like Alavarez and Nagler we adopt an approach based on the modeling of discrepancies between stated preferences and reported behavior, whilst taking into account the objective strategic context (c.f. Cain, 1978). The modelling approach, which utilizes repeated response data to identify latent preference classes in mixed multinomial logit models, is also substantially different and (as we show) more likely to provide reliable estimates. We draw upon data from the British Election Panel Study for the 1997 and 2001 General Elections in order to examine the extent of ‘non-preference voting’ broadly defined, and strategic voting, both subjectively and objectively defined. The approach both allows us to better represent preferences and voting for third or minor parties in a multiparty system, in this instance the British Liberal Democrats, and provides a more general framework for modelling party preference and voting behaviour. Modeling multiparty elections, preference classes and strategic voting 3 It has been argued previously that preference and vote are not equivalent and that voters are more likely to betray their preferences where the objective conditions dictate (Black, 1978; Cain, 1978). In other words voting contrary to one’s stated party preferences is related to the electoral context, or more precisely in the U.K., to the strategic situation in the constituency (electoral district), as this will shape the likelihood that a vote for a preferred candidate will be influential in the final outcome of the particular election or district. The rationale for this is straightforward: should a voter perceive a vote cast for their preferred candidate to be most likely wasted, that voter may opt to vote for another party. This is equally true in presidential elections where strategic voting may depend on the viability of the preferred candidate (e.g. Abramson et al, 1988). This is consistent with a rational choice approach and decision theory: McKelvey and Ordeshook and others have shown that a rational voter may vote against his or her most preferred party where it has little or no chance of winning in a multiparty election (McKelvey and Ordeshook, 1972; Cain, 1978). This can also be considered ‘Duvergian’ tactical voting (Fisher, 2004) as it is consistent with Duverger’s law which states that third or lowerplaced parties are deserted by rational voters in a single member simple plurality system (Riker, 1982, after Duverger, 1954). We would expect that strategic voting is more likely to affect smaller parties, as they are less likely to be considered viable, and parties in the political centre since (if preferences are single-peaked) they are more likely to be the second preference of voters on both the left and the right. Thus, in the case of Britain it is therefore unsurprising that strategic voting is particularly evident in the case of the Liberal Democrats (Spafford, 1972; Russell & Fieldhouse, 2004). Modeling multiparty elections, preference classes and strategic voting 4 However, research into recent British elections has tended to focus on the vote share between the two major parties, Labour (on the center-left) and Conservative (on the center-right). The third-largest party, Liberal Democrat (centrist), has often been ignored or cast as an influence on the other parties rather than as a straightforward alternative in its own right (e.g. Sanders, 1996). This is despite support for the Liberal Democrats being quite substantial, with around 20% of the vote share in general elections since the 1980s. Many of the simplifications taken when modeling multiparty elections have been driven by the availability of methodological tools for binary choices, where much analysis has been between just the top two parties or between a target party versus the remainder. This approach does not deal with the actual choices that voters face, however, and has been found to misestimate vote share between the larger parties in part because of the influence of the overlooked smaller party (Heath et al, 1991). More realistic modeling approaches must deal with the polytomous choice presented in multiparty elections. Multinomial logit (MNL) allows for the modeling of discrete choices with more than two alternative parties (e.g. Whitten & Palmer, 1996). However, it has been criticized because of its restrictive assumption of “independence from irrelevant alternatives” (IIA). With IIA the relative probability of choosing between any pair of alternatives must not depend on the presence (or absence) of other alternatives in the choice set. In effect, this assumption implies that voters must not view any parties as being clustered together, in the sense that the parties in the cluster could be seen as substitutes. This is patently not the case in British party politics, where the Liberal Democrats are currently seen as a Modeling multiparty elections, preference classes and strategic voting 5 closer substitute for the Labour Party than for the Conservative Party (Russell and Fieldhouse, 2004). Other authors have used multinomial probit (MNP) models, which allow for (limited) specification of a covariance structure for the disturbances and so do not impose the IIA assumption (e.g. Alvarez & Nagler, 1995; Alvarez, Nagler & Bowler, 2000). A recent review (Dow & Endersby, 2004) found little difference between MNL and MNP estimates when modelling the same UK multiparty election data, however. We use mixed multinomial logit (MMNL) models for our analyses. The advantage of MMNL is its flexibility; any discrete choice model consistent with random utility maximization can be approximated by a MMNL model (McFadden & Train, 2000). This is not the case for the standard MNP, where, for example, non-normally distributed random terms cannot be accommodated (Hensher & Greene, 2003). This is of significance later in this paper, where, because of non-normally distributed latent party preferences, an approximate non-parametric maximum likelihood estimator (NPMLE) solution is used to estimate latent classes of political preference. Preference and vote in the 1997 & 2001 general elections in England Data from two waves of the British Election Panel Study 1997-2001 (BEPS-2; Thomson et al 1999) were used. These waves, part of the 30-year, ongoing British Election Studies, were conducted shortly after the 1997 and 2001 general elections. Although the survey was also conducted in Wales and Scotland, only respondents living in England were Modeling multiparty elections, preference classes and strategic voting 6 utilized as they represented the largest group with the same choice set of three parties in each constituency – Conservative, Labour and Liberal Democrat. There were 2,551 respondents in the panel in the 1997 wave and 1,709 remaining in the 2001 wave. Only data from waves where individuals had a clear party of first preference and reported voting for one of the three major parties were retained. (Support for parties other than the main three was very limited; only 69 respondents reported voting for a different party, and an additional 17 said that they supported other parties even though they voted for a main party.) Further, 75 respondents with missing covariates (discussed later) were discarded. This resulted in 1,914 respondents contributing matched preferences and votes for 2,892 voting occasions. The BEPS-2 did not require respondents to explicitly rank-order the main parties in terms of preference. Instead, a ranking was constructed based upon party approval ratings and party identification. Respondents were asked to rate their current approval of each of the main parties on a 5-point scale from “strongly disapprove” to “strongly approve”. These ratings were then ranked to give a preference ordering. Because of the limited response options with a 5-point scale tied rankings were common. This was most probl