📈 economics

Donald Dewar’s mistake: Incomplete proportionality in the Scottish Parliament

This paper analyzes how Donald Dewar's choice of the Mixed-Member Proportional electoral system for the Scottish Parliament, intended to prevent single-party majorities, ultimately failed to ensure proportionality, leading to the SNP's 2011 majority and subsequent political hegemony due to path dependencies and election reversals.

Original authors: Iain McLean

Published 2026-10-16

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CC BY 4.0

Original authors: Iain McLean

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

In the study of how societies make collective decisions, political scientists examine the rules that turn individual votes into seats in a legislature. These rules are not merely administrative details; they act as the architecture of democracy, determining which voices are heard and which are silenced. One such rule is the mixed-member proportional system, a method designed to blend local representation with a fairer overall reflection of the public's will. The core idea is simple: voters cast two ballots, one for a local representative and another for a political party. The local winners take their seats, and then extra seats are added to the total to ensure that the final number of seats a party holds matches its share of the party vote. This system was adopted in Scotland in 1999 with a specific political goal: to prevent any single party from winning a majority of seats unless they won a majority of the votes, thereby forcing cooperation and protecting minority interests. The question that drives this research is whether the system worked as its creators intended, or if the mathematical machinery produced a different, and perhaps more consequential, reality.

The paper investigates the history of the Scottish Parliament, tracing the outcomes of seven elections from its creation in 1999 through to a projected result in 2026. The central finding is that the system, intended to be a barrier against single-party dominance, actually failed to stop the Scottish National Party from winning a majority of seats in 2011, despite that party receiving less than half of the total votes. This outcome was not a fluke but a structural consequence of the specific mathematical formula used to distribute the extra seats. The author, Iain McLean, argues that the choice of a particular calculation method, known as the d'Hondt formula, favored larger parties over smaller ones. This bias meant that when the Scottish National Party won a significant number of local seats, the formula did not compensate the smaller parties enough to balance the scale. As a result, the party secured 69 seats out of 129, a clear majority, on a vote share of roughly 45 percent.

This unexpected majority had profound historical consequences. Because the party had won a majority of seats, it felt compelled to honor a campaign promise to hold a referendum on Scottish independence, a step that would have been far more difficult to justify without that seat majority. The subsequent 2014 referendum, while rejecting independence, fundamentally shifted the political landscape, making the question of national identity the dominant force in Scottish politics. The paper further suggests that the system is prone to "election reversals," a situation where the group of parties that wins the most votes overall ends up with fewer seats than the opposing group. This happened in 2011 and is projected to happen again in 2026, where nationalist parties are expected to win a majority of seats despite receiving a minority of the total votes.

The research challenges the assumption that proportional representation systems automatically produce fair outcomes. By comparing the actual results with a hypothetical scenario using a different, more neutral mathematical formula, the study shows that the 2011 majority was fragile. If a different calculation method had been used, the Scottish National Party would have fallen just short of a majority, likely altering the course of the independence debate. The author also notes that the system's design, which divides the country into small regional districts rather than treating the nation as a single unit, limits the ability of the system to correct imbalances. In a single large district, a party needs only a tiny fraction of the vote to win a seat, but in Scotland's smaller regions, the threshold is higher, and the system struggles to accommodate the many small parties that emerge.

The paper concludes that the choice of electoral system was driven by political path dependency rather than deep technical understanding. The architects of the Scottish Parliament, particularly the Labour politician Donald Dewar, selected this system to prevent the Scottish National Party from gaining power, believing it was impossible for a party to win a majority of seats without a majority of votes. They were unaware of how the specific formula they chose would interact with the local political landscape. The study suggests that this lack of foresight, combined with the inherent bias of the d'Hondt formula, created a situation where the very mechanism designed to ensure stability and proportionality instead delivered a decisive, and historically transformative, majority to a party that did not command the support of most voters. The lesson is that the details of how votes are counted can have massive, unforeseen effects on the trajectory of a nation.

Technical Summary: Donald Dewar's Mistake: Incomplete Proportionality in the Scottish Parliament

Problem Statement
The paper investigates the unexpected outcomes of the Mixed-Member Proportional (MMP) electoral system adopted for the Scottish Parliament in 1999. The system was designed by Donald Dewar and the Labour government with two primary strategic objectives: first, to ensure that no party could secure a legislative majority without winning a majority of the popular vote; and second, to prevent the Scottish National Party (SNP) from achieving a hegemonic position that could trigger immediate negotiations for independence. The central puzzle is that the system failed to achieve these goals. Specifically, the SNP won an outright majority of seats in the 2011 election with only 44.7% of the total vote, and "election reversals" occurred in both 2011 and 2026, where unionist parties won a majority of votes but nationalist parties secured a majority of seats. Furthermore, the system proved less proportional than anticipated, particularly when compared to other MMP systems like those in New Zealand and Germany.

Methodology
The study employs a quantitative historical analysis of seven Scottish Parliament elections (1999–2026). The author utilizes official public domain data from the Electoral Management Board for Scotland, the Scottish Parliament, and BBC election results.

Key methodological components include:

Disproportionality Measurement: The paper calculates the Loosemore-Hanby (LH) index ( $D(LH) = 1/2 \sum |v_i - s_i|$ ) to measure the deviation between vote share ( $v_i$ ) and seat share ( $s_i$ ). This is calculated for the total vote, constituency votes, and regional votes separately.
Party System Metrics: The Effective Number of Parties (ENP) in both the electorate and the legislature is calculated using the Laakso-Taagepera index to track fragmentation and consolidation over time.
Comparative Analysis: The Scottish results are benchmarked against three other MMP jurisdictions (Germany, New Zealand, and Wales) to contextualize the level of proportionality.
Counterfactual Simulation: A specific analysis of the 2011 election is conducted by re-running the seat allocation using the Sainte-Laguë (Webster) divisor formula instead of the actual d'Hondt formula used in Scotland. This isolates the impact of the apportionment algorithm on the 2011 outcome.
Qualitative Classification: Parties are classified as "nationalist" or "unionist" based on manifesto analysis and public statements to determine the occurrence of election reversals.

Key Contributions and Results

Failure of the "Majority Protection" Mechanism:
The paper demonstrates that MMP did not prevent the SNP from winning a majority of seats (69 out of 129) with a minority of the vote (44.7%) in 2011. This outcome was the catalyst for the 2014 independence referendum, fundamentally altering the trajectory of Scottish politics.
The "Election Reversal" Phenomenon:
The analysis identifies two instances of election reversals where the faction with fewer total votes won a majority of seats.
- 2011: Unionist parties won more votes than nationalist parties, yet the SNP secured a majority of seats.
- 2026: A more pronounced reversal occurred where nationalist parties won 57% of seats on 41% of the vote, while unionist parties retained a majority of the popular vote.
Disproportionality and District Magnitude:
Contrary to the expectation that MMP ensures high proportionality, the Scottish Parliament exhibits significant disproportionality (mean LH index of 8.32). The paper attributes this to the relatively small District Magnitude (DM) of the regional lists (15–17 seats). Unlike New Zealand (DM=120) or Germany (where DM is calculated at the Land level), the Scottish regional DM is too small to fully compensate for the disproportionality of the First-Past-The-Post (FPTP) constituency component.
The Role of the d'Hondt Formula:
The counterfactual analysis of the 2011 election reveals that the use of the d'Hondt divisor formula, which biases allocation toward larger parties, was critical. Had the unbiased Sainte-Laguë formula been used, the SNP would have won 64 seats, falling just short of an absolute majority (65 needed). This suggests that the specific mathematical algorithm, rather than just the MMP structure, was the deciding factor in the 2011 hegemony.
Path Dependency in System Choice:
The paper argues that the choice of MMP over Single Transferable Vote (STV) was driven by path dependency and a lack of technical knowledge among Labour policymakers. Donald Dewar and the Scottish Constitutional Convention favored MMP to prevent an SNP majority but were unaware of the system's mechanics in New Zealand or Germany. They rejected STV due to internal Labour preferences and a lack of understanding of its properties, inadvertently selecting a system that allowed for the very outcome they sought to prevent.

Significance and Claims
The paper concludes that Donald Dewar's strategic calculations were fundamentally flawed. The claim is not that MMP is inherently flawed, but that its implementation in Scotland—with small regional districts and the d'Hondt formula—created a "perfect storm" for disproportionality.

The significance of the 2011 election is framed as a "foundation stone" of modern Scottish politics. The unexpected SNP majority forced the party to honor its "cheap talk" promise of a referendum, leading to the 2014 vote. Although independence was rejected, the event crystallized the constitutional question as the primary political cleavage, overriding traditional left-right divides. The paper posits that the 2016 Brexit referendum further shifted the balance, making the constitutional issue the dominant feature of the electorate, a state of affairs that the 2026 election results confirm.

Ultimately, the paper asserts that small technical details in electoral system design—specifically the choice between STV and MMP, and the choice between d'Hondt and Sainte-Laguë—can have profound, path-dependent consequences for national stability and constitutional outcomes. The author claims that the Scottish experience serves as a cautionary tale regarding the assumption that MMP automatically guarantees proportionality or prevents single-party dominance.

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