New research shows that when voters care about more than one issue, parliamentary elections can produce more representative and predictable policy outcomes than single-winner contests.
Most people assume that when an election comes down to two main parties, the logic of voting is straightforward: weigh up the options and choose the least bad one.
New research from King's Business School shows that this intuition holds in single-winner elections but breaks down in parliamentary contests once voters care about more than one policy issue.
In parliamentary elections, where policy is decided by legislative majorities rather than a single winner, voters behave strategically in ways that can significantly affect how parties compete and which policies are ultimately implemented.
Strategic or tactical voting is often assumed to arise only when there are three or more candidates. The research challenges this view, showing that voting behaviour depends on the type of election.
In single-winner elections, such as presidential or mayoral races, voters who agree with different candidates on different issues tend to support the candidate they prefer overall, rather than engaging in tactical voting.
Parliamentary elections operate differently, even when there are only two parties. When voters elect an MP, they are not choosing the final policy outcome directly. Policy is decided later, by votes in the legislature. A constituency only matters insofar as it helps change the national majority on a specific issue.
This distinction alters how rational voters behave.
The research, published in the American Economic Review, shows that in large parliamentary elections, voters who are conflicted across issues do not simply weigh up candidate platforms across multiple dimensions. Instead, they focus on a single consideration: which issue their constituency is most likely to influence at the national level.
They then base their vote on that issue alone, ignoring the others. The intensity of their preferences across issues plays little role. What matters instead is where an individual vote is most likely to affect the outcome.
Politicians are shown to anticipate this behaviour.
Because no group of voters is guaranteed to consistently support a given party, candidates can no longer ignore large sections of the electorate. This, in turn, encourages parties to adopt positions that reflect majority views across constituencies on each issue separately.
As a result, the research finds clear differences in outcomes. Parliamentary elections tend to produce outcomes that are more predictable and more representative than single-winner elections. When there is a policy option that most people would prefer over any alternative, parliamentary systems are more likely to select it. Presidential or mayoral systems often do not.
The broader implication is that electoral systems matter in subtle but important ways. Parliamentary elections do more than simply aggregate votes. They change how people vote and how politicians compete, leading to policies that better reflect what voters want across different issues.
We often think of tactical or strategic voting as something that only matters in multi-party elections. What this research shows is that in parliamentary elections, strategic voting is very much present, but works differently. Voters rationally focus on the single issue where their constituency is most likely to influence the national outcome. That behaviour, in turn, shapes how parties compete and helps ensure that the policies implemented reflect the will of the majority.
Dr Niall Hughes, Lecturer in Economics at King's Business School
You can read the full paper, Strategic Voting in Two-Party Legislative Elections, on the American Economic Review website.
