Abstract
This paper considers an electoral model in which an incumbent and a challenger have ideological policy preferences that are private information. The incumbent may bias pre-electoral policies to signal preferences to the electorate with the aim of affecting the outcome of the election. When the two candidates are of completely different types, such a policy bias can occur only in a moderate direction. However, when their possible types overlap, a policy bias can be created in either a moderate or an extreme direction.
1. Introduction
Although there are many cases in the political arena where politicians take moderate action to pander to median voters, there are also cases where they take action that may seem extreme, even to the eye of the vast majority of voters. On occasion, such extreme policies may ultimately enhance the popularity of the politician. Furthermore, there are cases where such phenomena emerge from a politically ‘murky’ situation in which the ideologies of ruling and opposition parties are not clearly divided.
For instance, after becoming prime minister in 2001, Junichiro Koizumi set out to enact market-oriented reforms in Japan. Although many Japanese, who had been fatigued by long-term economic stagnation, formed some degree of consensus around the need for decisive action to bolster the economy, a number of people were stunned by Prime Minister Koizumi’s reforms, which were accompanied by a slogan of ‘reform with no sacred cows’ and were radical by Japan’s standards (The Economist, 2006).
Astonishment reached its peak when he dissolved the House of Representatives after his bill to privatize Japan’s vast state-run postal service was rejected in the Upper House in 2005. Mr Koizumi called the general election, which essentially became a referendum on this privatization issue. People’s initial surprise turned to support for his administration, which manifested itself in the form of an electoral victory, and Mr Koizumi was re-elected prime minister.
An intriguing point is that the prime minister proceeded with the radical reforms even though he had not received monolithic support from the ruling parties, at least in his early days in office. Japan’s Liberal Democratic Party (LDP), to which Mr Koizumi belonged, had a considerable number of politicians who shared anti-market views with the bureaucrats at the main ministries (Mulgan, 2002: 55; Estévez-Abe, 2006). These conditions may have prompted him to make his declaration when taking office in 2001: ‘My reform plans would be tantamount to the destruction of the LDP (Mulgan, 2002: 49).’
Coincidentally, it seems that Mr Koizumi shared some of the political views of the opposition parties. There was a certain amount of policy commonality between him and some members of the opposition Democratic Party of Japan (DPJ), though they were not identical. Even though the LDP had traditionally been closer to business interests and the DPJ was closer to labor interests, the two major parties both contained a spectrum of views on the central issue of market-liberal reforms (Mulgan, 2002: 62). Out of such a muddled political environment emerged Mr Koizumi’s radical reform programs.
The purpose of this paper is to present a theoretical hypothesis that helps explain such extremism and sheds light on the relationship between interparty ideological differentiation and intraparty policy polarization. A fundamental question is this: Are pre-electoral policies more likely to become polarized when the ruling and opposition parties have distinct ideologies or when they share a degree of commonality? To address this question, this paper considers an electoral model in which an incumbent and a challenger compete against each other when their ideological preferences are private information. The focus is on pre-electoral policymaking by the incumbent that may be biased to signal preferences to voters. Behind this modeling selection is the author’s conjecture that Mr Koizumi might have been signaling his political philosophy to the electorate. Nonetheless, the model is completely abstract and does not deal with any concrete episodes.
The model makes a simple but novel assumption regarding the candidates’ ideological preferences. It allows the possible preferences of candidates from different parties to overlap. That is, it assumes that a candidate from a rightist party may have an ideal point that comes to the left of the most right-ideal point of a leftist party candidate. Under this assumption, it is shown that a policy bias can be created in either a moderate or an extreme direction, depending on conditions. By contrast, under a more standard assumption that the two candidates have completely different preferences, such a policy bias can occur only in a moderate direction.
To assume overlapping preferences to explain possible extreme actions may sound paradoxical. However, this assumption is actually not so unrealistic. Dewan and Spirling (2011) argue that the overlap condition is almost certainly present in all Westminster-type political systems. They estimate the ideal points for members of the British House of Commons by using their roll-call votes for the periods 1997–2001 and 2001–2005 that appear to have been free (i.e. not subject to party whips). With regard to the overlap, they report that approximately one third of the opposition party members were located to the left of the most right-wing member of the Labour Party, which was ruling during those periods. 1 Meanwhile, Kellermann (2012) uses early day motions (EDMs) instead of roll-call votes. EDMs can be interpreted as formal, non-binding expressions of opinion by members of the British House of Commons with parties exerting relatively little influence over signatures on them (Kellermann, 2012: 760–1). He develops a statistical model of EDM signing behavior and uses it to estimate the preferences of the legislators. The result exhibits a similar overlap pattern of ideal points.
Even in the United States, where the two major parties are usually supposed to have distinct ideologies, there are cases where congressional representatives from the two parties will take the same action on a legislative bill. In addition, from the theoretical standpoint of this model, even if there is the slightest possibility of overlapping ideologies, the result obtained below will not be affected as long as separating equilibrium is focused on. This point will be touched on at the end of Section 5.
There is a growing literature on candidate signaling behavior in elections. One strand of this literature focuses on pre-electoral platforms announced by candidates. Banks (1990) and Harrington (1992) derive conditions under which campaign promises are able to convey some sort of correct information about the candidate’s preferences. Kartik and McAfee (2007) develop an electoral model in which candidates may signal their character, an unobservable trait with which they implement what they believe without pandering to the electorate. Callander and Wilkie (2007) establish equilibria when candidates have different incentives to misinform voters about their preferences. In Callander’s (2008) model, politicians may signal that they are policy-motivated, rather than office-motivated.
Another strand of the literature, to which this paper contributes, analyzes electoral models in which incumbents seeking re-election signal some information via their pre-electoral behavior in office. There are several models in which politicians signal their competence (e.g. Rogoff and Sibert, 1988; Canes-Wrone et al., 2001; Ashworth and Shotts, 2010; Fox and Stephenson, 2011). Some politicians may choose ‘populist’ policies when they wish to be perceived as honest, rather than corruptible (Acemoglu et al., 2013). Morris (2001) and Maskin and Tirole (2004) analyze incentives to signal congruence with voter preferences. Morelli and Van Weelden (2013) extend the Maskin–Tirole model and find that policymakers are likely to pander to public opinion on ‘doorstep issues’, on which politicians do not have great informational advantages over voters.
Schultz’s (2002) model is most similar to the one in this paper in terms of its structure. He analyzes a situation in which policymakers have private information about two dimensions (i.e. their ideological preferences and the state of the economy) and may bias their policies to signal such information. Schultz shows that uncertainty about the state of the economy leads to extreme policies, while uncertainty about the incumbent’s preferences leads to moderate policies.
Thus, in Schultz’s model, the extreme-policy result is not generated by uncertainty about preferences. One of the factors behind this conclusion is in the following assumption which he makes with regard to ideological preferences: the ideology level of non-government candidates is less than that of moderate-type incumbents which is less than that of extreme-type incumbents. That is, candidate preference types are clearly divided.
The model developed in the current paper simplifies Schultz’s model in a certain sense. It narrows the focus to situations where a politician sends signals regarding unknown parameters of one dimension, namely, ideology, and examines in full detail the various possibilities related to such parameters. Specifically, it shows that extreme-policy results can be obtained without introducing two-dimensional uncertainties if we assume overlapping ideology types. To the best of the author’s knowledge, there is no electoral-competition model that makes this assumption. Cukierman and Tommasi (1998), like Schultz (2002), assume that ideology types do not overlap: candidate R is always perceived to be the right-wing candidate. By contrast, in many papers that analyze the informational role of platforms, such as Harrington (1992) and Banks (1990), the two candidates are treated symmetrically, so situations are often tackled where the sets of possible types of candidate are identical. It is worthwhile to analyze a case lying between these two polar scenarios.
The rest of the paper is organized as follows. Section 2 explains the set-up and Section 3 briefly examines the standard case with non-overlapping types. Section 4 analyzes voter decisions and Section 5 examines the incumbent’s signaling behavior and derives central results. Section 6 concludes the paper.
2. Set-up of the model
This paper considers a spatial electoral model that is admittedly very simple. There are N voters and two candidates (L from a leftist party and R from a rightist party). To avoid unnecessary complications related to a tie-breaking rule, N shall be an odd number. Without loss of generality, the incumbent is supposed to be from the rightist party (R) and the challenger from the leftist party (L). 2 We use female pronouns for the incumbent and challenger and male pronouns for voters. As will be specified below, the voters as well as candidates, L and R, have their respective ideological preferences for policies. As in Banks (1990), it is assumed that the ideologies that voters harbor are common knowledge but that the ideologies to which the two candidates adhere are private information. 3
The timing of the game is as follows. Nature picks the two candidates’ ideology types independently. This is private information. Incumbent R implements a policy in the first period. Voters observe the policy action and update their beliefs concerning the incumbent’s ideology. They then vote for either candidate L or R. After the election, the candidate obtaining the majority of votes implements a second-period policy.
Because this is a two-period model, the winner is expected to adopt her ideal policy in the second period. The focal points of the model are the policy taken in the first period and the election results. The incumbent may bias the first-period policy, being conscious that her policy choice could transmit a signal regarding her ideology to the electorate and affect the upcoming election results.
The utility of voter
where
If the issue is about income redistribution, a micro-foundation behind equation (1) can be provided using a simplified version of a redistributive-politics model developed by Dixit and Londregan (1998). In this case,
The pay-off for candidate P (P = L, R) in period t is assumed to have the form
where V is a constant perquisite only a politician in office can receive, and
We now introduce uncertainty regarding the candidates’ ideologies. Candidates L and R have possible ideology types
Based on the motivation described in the Introduction, we mainly analyze the overlapping-type case:

Ideal policies.
The following assumption is not essential but is made to avoid unnecessarily increasing the number of situations to be considered.
To investigate voter behavior in detail, the values A, B, C, D, and E are defined as (see Figure 1)
From now on, a candidate with, say, bliss point
3. A non-overlapping-type case
Before starting the main analysis, we briefly look at the situations under the standard assumption: possible types of candidates L and R do not overlap (i.e.
The key idea is that the incumbent R would like to signal her own type to the median voter if doing so increases the chance of her re-election. In this respect, if the median voter favors a relatively small policy (i.e.
Suppose, by contrast, that the median voter is tilted toward the right (i.e.
4. Voter decisions at polls
Returning to our main assumption of overlapping types, voter decisions are examined. After observing the first-period policy, each voter updates his beliefs about incumbent R’s type from the prior
The second-period policy is chosen by the winner of the election. This is done without further concern for elections. When candidate
If the above inequality holds with <, then this voter votes for R with certainty. Replacing the inequality by an equality and using equation (1) yields an equation that represents a straight line in (r, l) space (Figure 2). If the posterior pair (r, l) falls on this line, voter i becomes indifferent about the two candidates and makes his decision by tossing a fair coin. Thus, this straight line is called voter i’s indifference line. If the posterior pair (r, l) falls in the shaded area in Figure 2, then voter i votes for candidate L; if it falls in the non-shaded area, they vote for candidate R.

Voters’ decisions.
The following lemma tells us how the indifference line shifts when voter i’s ideal policy rises. The proof of the lemma, as well as the precise form of the indifference line, is in Appendix 1.
Lemma 1. Voter indifference line
Voter i’s indifference line rotates around a fixed point
For example, Figure 2(d) illustrates voter i’s indifference line as a bold straight line when his bliss point comes to some
The following lemma states that the outcome of the election depends upon the behavior of the median voter. A sketch of the proof is in Appendix 2.
Lemma 2. Median voter’s decisiveness
For the incumbent R who pursues majority votes, the median voter m is decisive in the sense that his voting behavior determines the outcome of the election.
This result is not trivial because the monotonicity in voters’ preferences for candidates is violated here. For instance, if the posterior pair (r, l) is close to the origin in Figure 2, the voter preference switches from candidate L to R as his bliss point
Taking Lemma 2 into account, we focus on the median voter’s behavior. The belief of the voters about the challenger’s type is summarized by
For instance, suppose that the median voter’s ideal policy satisfies
However, if
5. Incumbent R’s signaling behavior
In this electoral game, the incumbent faces the following trade-off. On the one hand, she wishes to be re-elected because, if she is, she can gain a perquisite and achieve her ideal policy in period two. Thus, she may wish to bias her first-period policy if such a bias increases the odds of re-election. On the other hand, she does not want to bias her first-period policy too much because she does not want to reduce her first-period pay-off excessively.
Incumbent
The focus here is the policy in period one. If information were complete,
There are three cases to be considered.
5.1. Case 1: when
If
Proposition 1. Outcomes in Case 1
Suppose that
The last part of the proposition follows from the inspection of Figure 2.
5.2. Case 2: when
and
In this case, the extreme incumbent can have an incentive to mimic the moderate type, because she can be re-elected by signaling a small r. From Figures 2(a) to (f), it follows that in this case
An example of this case is in Figure 2(d), as seen above.
Based on the above consideration, Figure 3 illustrates the incumbent’s indifference loci in

Candidate R’s indifference loci in Case 2.
In Case 2, we define
The solution concept used in the model is the perfect Bayesian equilibrium (PBE). Usually, when a signal-sender’s indifference loci have standard shapes of continuous curves and satisfy the single-crossing property, Cho and Kreps’s (1987) Intuitive Criterion selects the most Pareto-efficient separating PBE (i.e. the Riley outcome). In the current model, however, the sender’s indifference loci satisfy neither of the above conditions, and hence the Intuitive Criterion does not isolate a unique outcome. 8 Nevertheless, this model focuses on the Riley outcome for the reason below. A sketch of the proof is in Appendix 4.
Lemma 3. Equilibrium
(i) When attention is restricted to separating equilibria, the Intuitive Criterion always selects a unique outcome (the Riley outcome). (ii) When the focus is on pooling equilibria, there exists no PBE per se under some parametric assumptions (e.g.
In short, because neither pooling nor hybrid equilibria can solve the problems of non-existence, this model focuses on separating equilibrium. A partial characterization of pooling and hybrid equilibria is provided in Appendix 4.
Another reason for this focus comes from the fact that if some uncertainty on the side of voters is introduced (under somewhat awkward assumptions), the sender’s indifference loci exhibit standard continuities and the Intuitive Criterion selects a unique separating outcome. This point is revisited at the end of this section.
The proof of part (i) of Lemma 3 directly derives the following proposition, in which the incumbent’s first-period policy and the election outcome in the intuitive separating outcomes are characterized. In what follows, the term bias in policy is used to indicate some difference in policy compared with that chosen under complete information.
Proposition 2. Outcomes in Case 2
Suppose that
Intuitively, in Case 2, the incumbent can be re-elected if she signals to the voters that she has a high probability of being moderate, as seen above. If, in addition, the incumbent’s types are relatively similar (i.e.
Note that, from an inspection of equation (A.1) in Appendix 3, it follows that
The above logic for a policy bias is the same as that under the standard assumption, as explained in Section 3. The importance of our novel assumption of overlapping types is highlighted in Case 3, as seen in the next subsection.
5.3. Case 3: when
and
In this case, the incumbent can be re-elected by signaling a large, not small, r. An example is found if the median voter’s bliss point is as in Figure 2(g) and if
In Case 3, the probability with which R wins the election is
in contrast to equation (4). This situation can be analyzed using Figure 4, which seems to be obtained by turning Figure 3 upside down. In Figure 4,

Candidate R’s indifference loci in Case 3.
Proposition 3. Outcomes in Case 3
Suppose that
That is, a policy bias can also occur in the extreme (upward) direction when the possible types of the candidates overlap. The reason for this result is that we may have a situation in which even an extreme type,
The above result contrasts with that under the standard assumption of non-overlapping types. An intuitive reason why a bias in extreme directions does not occur in the standard case was explained in Section 3. Technically, if the types do not overlap, as in Figure 1(b), then the central point,
Returning to the extreme-policy result, because the incumbent’s rightist policy is predicted when the median voter is tilted toward the right, it can be said that their interests are not completely in conflict. However, Proposition 3 shows that a small change in the median voter’s position can cause a magnified effect on a politician’s behavior through the politician’s signaling intention. Indeed, it is worth noting that her pre-electoral policy can be extreme to a degree that nobody desires. Suppose, for instance, that the largest ideal policy among the whole electorate,
A partial justification for the assumption that the candidates’ types may overlap was given in the Introduction. We point out here that, from a theoretical viewpoint, even if the probability of such an overlap is very small, the result obtained above is not affected. To see this, note that the prior belief
This model focuses on separating equilibrium, instead of pooling or hybrid equilibria, using the reasoning in Lemma 3. Another justification for this focus comes from the result of a modified version of the model as follows. Suppose there is mutual uncertainty between candidates and voters, so that a voter preference for candidates is also private information. It might then be problematic to assume that every voter’s preference is uncertain because it may become difficult to determine the identity of the median voter. The simplest way to avoid this problem is to assume that there are only three voters, i =1, 2, 3, and that only voter number two has uncertainty. The probability of the incumbent being re-elected then depends upon the probability with which she can attract this median voter. Under this set-up, it is possible to construct a smooth indifference locus for the incumbent and show that the Intuitive Criterion selects a unique outcome, the Riley outcome.
Finally, if the incumbent is from a leftist party, the prediction is completely symmetric. An extremely leftist policy can be predicted when the opposite conditions to those in the envy case of Proposition 3 are satisfied.
6. Concluding remarks
This paper has shown that an incumbent’s signaling behavior is not limited to distorting her policy to moderate directions even if private information is introduced on only one-dimensional parameters: the candidate ideologies. This result contrasts with that of Schultz (2002), in which extreme policies were caused by uncertainty about an additional parameter: the state of the economy. The key assumption in our model is that possible ideology types of candidates from different parties overlap. Because this is a novel assumption, the model devoted a considerable amount of space to the proofs of basic results (e.g. the median voter’s decisiveness) with the help of figures.
One implication of the model is that the extremist tendency within any one party may become most active when party ideologies are overlapping. Conversely, pre-electoral signaling motives would inevitably generate moderation between parties when the ruling and opposition parties have completely distinct ideologies. Although this prediction can motivate empirical research, there will be at least one serious difficulty associated with such a study. Because extremism needs to be measured by policy divergence from an incumbent politician’s ideal, an estimate of her bliss point would be required. This is conceptually challenging because such bliss points cannot be gauged simply by reference to her actual actions. A possible way to estimate them may be to distinguish her pre-electoral and post-electoral policies, as implied by the model. Empirical analyses overcoming such difficulties may be a useful subject for future research.
Footnotes
Appendix 1. Proof of Lemma 1
The condition under which voter i votes for L with certainty (equation (3)) can be rewritten as follows, with the use of equation (1):
Voter i’s indifference line is then defined as
where
That is, any voter’s indifference line passes through the point
Next, if voter i’s ideal policy rises, the intercept of the indifference line for that voter decreases (Figure 2)
except for the point in which H becomes zero and K/H becomes discontinuous (i.e. when
Appendix 2. Sketch of the proof of Lemma 2
First, we prove the following claim.
(Proof of Claim 1)
From the definitions of K and H in Appendix 1,
By l’Hopital’s rule,
Claim 1 indicates that voter i’s indifference line rotates by less than
Next, we prove Lemma 2. There are four cases to be considered: (1)
Suppose, in addition, that R signals some
As seen above, whether R can win the votes of voters who belong to (i) and (iv) by signaling some
Next, suppose that R signals
Finally, suppose that R signals some
If
Appendix 3. Derivations of x ¯ 1 * ( β R ) and x ¯ 1 * ( β R )
The pay-off that candidate
The smaller (respectively, larger) solution is denoted by
Appendix 4. Sketch of the proof of Lemma 3
Here,
In addition, let
(Proof of Claim 2)
In Figure 3, this claim implies that, for each type
(Proof of Claim 3)
Differentiating
As
Now we prove the lemma.
Acknowledgements
The author wishes to thank Claudio Mezzetti, Yoichi Hizen, Yuma Kawahara, Takashi Narihiro, Rodney Dunham, two anonymous referees and the editor for helpful comments. The usual disclaimers apply.
Declaration of conflicting interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by JSPS KAKENHI (grant number 24530301).
