Year 9 OCR Politics: Formula & Theorem Quick Reference Manual | 九年级OCR政治：公式定理速查手册

📚 Year 9 OCR Politics: Formula & Theorem Quick Reference Manual | 九年级OCR政治：公式定理速查手册

Welcome to the OCR Year 9 Politics quick reference guide. This handbook compiles the most important formulas, theorems, and quantitative rules that underpin the study of elections, voting systems, and political power. Whether you are calculating the distribution of seats, evaluating the fairness of an electoral outcome, or analysing strategic voter behaviour, these tools will help you build a solid foundation in political analysis.

欢迎使用 OCR 九年级政治速查手册。本手册汇集了支撑选举、投票制度和政治权力研究的最重要的公式、定理和量化规则。无论你是在计算席位分配、评估选举结果的公平性，还是分析选民的策略行为，这些工具都将帮助你打下坚实的政治分析基础。

1. Median Voter Theorem | 中位选民定理

The median voter theorem predicts that in a majority-rule election where preferences are single-peaked and arrayed along a single dimension, the outcome will reflect the ideal point of the median voter. Candidates and parties therefore have an incentive to move their platforms towards the centre to capture the largest share of votes. The theorem also explains why radical platforms often lose support: they are distant from the decisive median position.

中位选民定理预测，在偏好呈单峰且沿单一维度排列的多数决选举中，结果将反映中位选民的理想点。因此，候选人和政党有动力将其竞选纲领向中间靠拢，以争取最大份额的选票。该定理也解释了为何激进纲领常常失去支持：它们远离决定性中位立场。

Policy outcome = Median(voter ideal points)

政策结果 = 选民理想点的中位数

Imagine a constituency where voters’ preferred tax rates are 10%, 25%, 40% and 70%. The median is between 25% and 40%; the candidate closest to that range generally wins.

设想一个选区，选民偏好的税率分别为 10%、25%、40% 和 70%。中位数介于 25% 与 40% 之间；最接近该区间的候选人通常获胜。

2. Duverger’s Law | 杜瓦杰定律

Duverger’s law states that the single-member plurality (first-past-the-post) electoral system tends to favour a two-party system. The mechanical effect reduces the seats of smaller parties because they rarely win constituency races, while the psychological effect discourages voters from ‘wasting’ their votes on unlikely winners, reinforcing duopolistic competition. In contrast, proportional representation systems tend to produce multiparty systems, a tendency sometimes called Duverger’s hypothesis.

杜瓦杰定律指出，单名选区简单多数制（得票最多者当选）的选举制度倾向于产生两党制。机械效应减少了小党的席位，因为它们很少赢得选区竞选，而心理效应则抑制选民将选票投

Published by TutorHao | Year 9 政治 Revision Series | aleveler.com

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