Electoral Systems and Party Systems

1. Electoral Systems are the Foundation of Representative Democracy

An electoral system is the most fundamental element of representative democracy, translating citizen’s votes into representive’s seats.

Core democratic function. Electoral systems are the indispensable machinery by which citizens' votes are transformed into legislative representation. This process is not merely technical; it is the bedrock upon which the legitimacy and functionality of a representative democracy are built. The choice of an electoral system profoundly influences who gets elected and how power is distributed.

Systematic analysis. This study meticulously examines 70 distinct electoral systems employed across 27 established democracies between 1945 and 1990. By analyzing 384 national legislative and European Parliament elections, it provides a comprehensive empirical foundation for understanding the practical consequences of different electoral designs. The goal is to demystify these systems, revealing that they are often less diverse and complex than commonly assumed.

Beyond simple mechanics. While seemingly a technical detail, the electoral system is also a potent instrument for democratic reformers. It can be deliberately designed or adjusted to achieve specific political outcomes, such as enhancing proportionality, fostering stable governments, or ensuring minority representation. Understanding its mechanics and effects is crucial for anyone seeking to shape the political landscape.

2. Four Core Dimensions Shape Electoral Outcomes and Party Systems

The electoral formula, the number of representatives elected per district, electoral thresholds, and five other key features of electoral systems on the proportionality of the election outcome, the degree of multipartism, and the creation of majority parties.

Defining the framework. The study identifies four primary dimensions that fundamentally determine an electoral system's impact: the electoral formula, district magnitude, electoral threshold, and assembly size. These elements, when combined, dictate how votes translate into seats and, consequently, influence the nature of the party system.

Interconnected variables.

• Electoral Formula: Dictates the mathematical method for allocating seats (e.g., plurality, proportional representation, semi-proportional).
• District Magnitude: The number of representatives elected from each constituency. A higher magnitude generally leads to greater proportionality.
• Electoral Threshold: The minimum percentage of votes a party needs to win seats, either legally mandated or implicitly determined by other factors.
• Assembly Size: The total number of seats in the legislature. Larger assemblies tend to allow for more proportional outcomes.

Beyond the basics. While these four are central, other factors like ballot structure, malapportionment, presidentialism, and inter-party electoral links (apparentement) also play a role, albeit often secondary. The interplay of these dimensions creates a complex but ultimately decipherable set of relationships that govern electoral outcomes and party system characteristics.

3. The "Effective Threshold" is the Most Potent Determinant of Proportionality

My main conclusions will be that, of the five dependent variables, disproportionality is the one that can be explained best in terms of the electoral system characteristics, and that the strongest explanation of the various dependent variables is provided by what I shall call the ‘effective threshold’, a combination of district magnitude and electoral thresholds.

A unified measure. The "effective threshold" emerges as the single most powerful explanatory variable for electoral disproportionality. This innovative concept synthesizes the impact of both legal electoral thresholds and district magnitude into a single, quantifiable percentage. It represents the practical barrier a small party faces in gaining representation, regardless of whether that barrier is explicit in law or implicit in the electoral geography.

Direct and dramatic impact. A higher effective threshold directly correlates with greater disproportionality, meaning a larger gap between a party's vote share and its seat share. This is because higher thresholds systematically disadvantage smaller parties, making it harder for them to translate their votes into seats. Conversely, lower effective thresholds lead to more proportional outcomes, ensuring a fairer distribution of seats according to votes.

Explaining the variance. The effective threshold alone accounts for a substantial portion of the variance in disproportionality across different electoral systems. Its predictive power surpasses that of other individual dimensions, highlighting its critical importance for electoral engineers aiming to fine-tune the proportionality of an election's outcome.

4. Electoral Formulas and Assembly Size Also Significantly Impact Proportionality

The effect of the electoral system on multipartism is more modest but still very important, and the explanatory power of the other electoral system variables—the electoral formula, assembly size, apparentement, ballot structure, and presidentialism—is also more modest but, again, not at all negligible.

Beyond the threshold. While the effective threshold is paramount, the electoral formula and assembly size are also significant, albeit secondary, instruments for influencing proportionality. Different formulas inherently favor different outcomes:

• D'Hondt: Least proportional among PR formulas, systematically favoring larger parties.
• LR-Hare: Most proportional, treating all parties more even-handedly.
• Modified Sainte-Lague, LR-Droop, STV: Intermediate in proportionality.

The role of scale. Assembly size, the total number of seats in the legislature, also plays a crucial role. Larger assemblies generally allow for greater proportionality because there are more seats to distribute, making it easier to reflect vote shares accurately. Conversely, very small assemblies inherently limit proportionality, even with the most proportional formulas.

Combined influence. When combined with the effective threshold, these factors provide a robust framework for understanding and predicting the degree of disproportionality. Electoral engineers can manipulate these dimensions to achieve desired levels of proportionality, balancing the representation of diverse political views with other goals like governmental stability.

5. Plurality Systems Guarantee Majorities, While PR Systems Foster Multipartism

Clearly, the effective threshold is a strong instrument for electoral engineers, but the plurality formula (with its inherently very high effective threshold) is the strongest instrument.

Fundamental divide. The most striking distinction in party system outcomes lies between majoritarian (especially plurality) and proportional representation (PR) systems. Plurality systems, characterized by their inherently high effective thresholds, are exceptionally effective at generating single-party parliamentary majorities. This often occurs even when the winning party does not secure a majority of the popular vote, leading to "manufactured majorities."

Multipartism in PR. In contrast, PR systems, designed for proportionality, naturally lead to a greater number of parties gaining representation, thus fostering multipartism. While PR systems can still produce majorities, these are far less frequent and are rarely "manufactured" in the same way as in plurality systems. The degree of multipartism within PR systems, however, varies depending on the specific formula and threshold.

Strategic behavior. The stark difference in outcomes is partly due to strategic voting. In plurality systems, voters are strongly incentivized to vote for larger parties to avoid "wasting" their vote on smaller parties with little chance of winning. This psychological effect further consolidates the party system into a two-party or two-bloc configuration, a phenomenon less pronounced in PR systems where votes are less likely to be "wasted."

6. Electoral Systems Primarily Influence Parliamentary Parties, Not Elective Parties

The conclusion is now inescapable that differences in disproportionality in PR systems do not appreciably affect the effective number of elective parties.

Mechanical vs. psychological effects. Electoral systems exert a more pronounced influence on the composition of the legislature (parliamentary parties) than on the initial preferences of the electorate (elective parties). This distinction highlights Maurice Duverger's concepts of "mechanical" and "psychological" effects. The mechanical effect refers to how votes are directly translated into seats, while the psychological effect describes how voters and elites strategically adjust their behavior based on anticipated outcomes.

Limited psychological impact in PR. The study finds that within PR systems, changes in electoral rules, even those affecting proportionality, do not significantly alter the effective number of elective parties. This suggests that voters' and elites' strategic calculations (psychological factors) are less sensitive to the nuances of PR formulas and thresholds. The number of parties voters choose to support remains relatively stable.

Strong mechanical impact on parliament. However, the mechanical effect of the electoral system on the effective number of parliamentary parties is substantial and consistent. Even if voters' initial preferences don't shift much, the way votes are counted and seats are allocated directly shapes the legislative landscape. This means that while PR systems may not drastically change voter behavior, they are highly effective in determining the actual party composition of parliament.

7. Ballot Structure, Presidentialism, and Apparentement Offer Additional Nuances

Apparentement therefore joins ballot structure and presidentialism as important influences on disproportionality and/or the party system that have been discovered in this chapter.

Beyond the core dimensions. While the effective threshold, electoral formula, and assembly size are the primary drivers, three other variables—ballot structure, presidentialism, and apparentement—also contribute to shaping electoral outcomes and party systems. These factors introduce subtle but measurable influences.

Specific impacts:

• Ballot Structure (Ordinal vs. Categorical): Ordinal ballots (allowing voters to rank or split votes across parties) tend to reduce the frequency of manufactured majorities, particularly in majoritarian systems, by encouraging more sincere voting.
• Presidentialism: In fully presidential systems, especially with concurrent plurality elections, the focus on the presidency significantly reduces the effective number of elective parties and increases the likelihood of parliamentary majorities. This effect is not observed in semi-presidential or ceremonial presidencies.
• Apparentement (Inter-Party Electoral Links): Formal alliances between party lists allow smaller parties to pool votes, thereby reducing disproportionality. While its impact on the number of parties is less clear, it consistently improves the proportionality of seat allocation.

Refining the picture. These additional variables, though less impactful than the core dimensions, demonstrate the multifaceted nature of electoral system design. They offer further avenues for fine-tuning outcomes, particularly in specific political contexts, and highlight how seemingly minor rules can have discernible effects.

8. Electoral Systems Exhibit High Stability, Yet Trends Favor Greater Proportionality

One of the best-known generalizations about electoral systems is that they tend to be very stable and to resist change.

Inertia and resistance to change. Electoral systems are remarkably stable, often remaining unchanged for decades. Fundamental shifts, such as moving between majoritarian and proportional representation, are exceedingly rare, with France being the only country in the study to oscillate between these two types. This stability is often attributed to entrenched partisan interests and institutional conservatism.

Incremental evolution. Despite this overall stability, many countries do undertake significant, albeit not revolutionary, adjustments to their electoral laws. These changes, often involving modifications to thresholds, formulas, or the introduction of two-tier systems, are frequent enough to generate a rich dataset for comparative analysis.

A clear direction. A discernible trend among the democracies studied is a move towards greater proportionality. This is evident in:

• The universal abolition of multi-member districts in plurality systems.
• The increasing adoption of two-tier districting in PR systems.
• Shifts from less proportional (d'Hondt) to more proportional (LR-Hare, modified Sainte-Lague) formulas within PR.
• The introduction of national legal thresholds, often at moderate levels (4-5%).

This trend suggests a growing normative preference for electoral justice and broader representation, particularly within countries already committed to PR principles.

9. Electoral Engineering is a Powerful Tool, But with Inherent Limits

What is the practical significance of the analysis presented in this volume for electoral engineers? In a frequently cited statement, Giovanni Sartori characterizes the electoral system as ‘the most specific manipulative instrument of politics’.

Potent but not omnipotent. The study confirms that electoral systems are indeed powerful instruments for shaping political outcomes, particularly in controlling disproportionality and influencing the structure of party systems. Electoral engineers have a clear understanding of how to adjust key dimensions like the effective threshold, electoral formula, and assembly size to achieve desired levels of proportionality.

Limits to manipulation. However, the power of electoral engineering is not absolute. A significant portion of the variance in electoral outcomes remains unexplained by electoral rules alone, influenced by broader socio-political factors like societal cleavages, group sizes, and regional vote distribution. Furthermore, the influence on the effective number of elective parties (voter behavior) is notably weaker than on parliamentary parties (seat distribution).

Ethical considerations. The stability of electoral systems also highlights a crucial constraint: changes should not be undertaken for narrow partisan gain. Frequent, self-serving alterations, as seen in some countries, undermine the legitimacy of the democratic process. For established democracies, reforms are best approached as incremental improvements, while new democracies have a unique opportunity to design systems from the ground up with clear objectives.

10. Five Exemplary Devices Offer Models for Effective Electoral Reform

In addition, however, there are a number of specific devices used in some of our electoral systems that appear to work particularly well and that deserve to be recommended as models for electoral engineers elsewhere.

Practical lessons for reformers. The study identifies five specific electoral devices that have proven particularly effective in achieving desirable outcomes, offering valuable models for electoral engineers:

1. Two-Tier Districting in PR Systems: This combines the benefits of local accountability (small lower-tier districts) with national proportionality (large upper-tier adjustment seats). It also effectively eliminates malapportionment and gerrymandering.
2. Two-Tier Districting for Plurality Systems: A novel proposal to guarantee parliamentary majorities for the plurality winner while maintaining local representation. This also addresses malapportionment and incentivizes nationwide campaigning.
3. National Legal Thresholds (Percentage-Based): Simple, clear thresholds expressed as a percentage of the national vote avoid arbitrary exclusions based on geographical vote distribution, ensuring that only parties with genuine national support gain representation.
4. Transferability of Votes (e.g., STV): This mechanism, where surplus or defeated votes are reallocated, significantly enhances proportionality by minimizing wasted votes. It is recommended for systems like Japan's SNTV or Finland's open-list PR to improve accuracy.
5. Apparentement (Inter-Party Electoral Links): Allowing parties to formally link their lists for seat allocation enables smaller parties to overcome the inherent bias against them in many PR systems, fostering alliances and improving overall proportionality without requiring mergers.

These recommendations provide concrete, actionable strategies for enhancing the fairness, stability, and representativeness of electoral systems.

Last updated: March 8, 2026