science

Roemer model of political competition

Roemer model of political competition is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Roemer model of political competition rather than just read about it. In short: The Roemer model of political competition is a game between political parties in which each party announces a multidimensional policy vector. Since Nash equilibria do not normally exist when the policy space is multidimensional, John Roemer introduced the concept of party-unanimity Nash equilibrium (PUNE), which can be considered an application of the concept of Nash equilibrium to political competition.

Key takeaways

Roemer model of political competition belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Roemer model of political competition to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Roemer model of political competition from memory before moving on to harder problems.

Reference excerpt

The Roemer model of political competition is a game between political parties in which each party announces a multidimensional policy vector. Since Nash equilibria do not normally exist when the policy space is multidimensional, John Roemer introduced the concept of party-unanimity Nash equilibrium (PUNE), which can be considered an application of the concept of Nash equilibrium to political competition. It is also a generalization of the Wittman model of political competition. In Roemer's model, all political parties are assumed to consist of three types of factions—opportunists, militants, and reformers. Opportunists seek solely to maximize the party's vote share in an election; militants seek to announce (and implement) the preferred policy of the average party member; and reformers pursue a compromise between the aims of opportunists and militants, combining concerns for electoral success with fidelity to the party’s ideological preferences. It has been shown that the existence of reformers has no effect on what policies the party announces. With two parties, a pair of policy announcements constitute a PUNE if and only if the reformers and militants of any given party do not unanimously agree to deviate from their announced policy, given the policy put forth by the other party. In other words, if a pair of policies constitute a PUNE, then it should not be the case that both factions of a party can be made weakly better off (and one faction strictly better off) by deviating from the policy that they put forward. Such unanimity to deviate can be rare, and thus PUNEs are more likely to exist than regular Nash equilibria.

Existence of PUNEs Although there are no known cases where PUNEs do not exist, no simple necessary and sufficient conditions for the existence of non-trivial PUNEs (i.e., in which no party offers the ideal policy of either its militants or opportunists) have yet been offered. The question of the existence of non-trivial PUNEs remains an important open question in the theory of political competition.

See also Electoral competition Investment theory of party competition

References

John E. Roemer, Political Competition: Theory and Applications (2001) Cambridge, MA: Harvard University Press.

Worked examples

Example 1 — a first encounter with Roemer model of political competition

Start with the simplest possible case. Write down what Roemer model of political competition claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Roemer model of political competition before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Roemer model of political competition ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Roemer model of political competition

In research: Roemer model of political competition appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Roemer model of political competition in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Roemer model of political competition is common in secondary-school and first-year university syllabi. It links to neighbouring topics Game theory, Political theories, so understanding it makes those chapters shorter.
In everyday life: Look for Roemer model of political competition outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Roemer model of political competition in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Roemer model of political competition means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Roemer model of political competition out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Roemer model of political competition in simple terms?

Why does Roemer model of political competition matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Roemer model of political competition?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Roemer model of political competition.