Mathematical Economics 2: Chapter 1 Overview

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Questions and Answers

What is the primary assumption in the basic random network formation model discussed in the text?

  • Link formation occurs through a completely deterministic process.
  • Links are formed to optimize network efficiency.
  • Links are formed based on pre-existing social ties.
  • A completely random process is responsible for link formation. (correct)

What serves as a key purpose of studying random networks within the context described?

  • To serve as a benchmark against which real-world networks are compared. (correct)
  • To replace social network analysis with mathematical models.
  • To demonstrate the mathematical impossibility of social networks.
  • To show the superiority of random networks over observed networks.

Which of the following properties are typically studied in random networks?

  • How links are distributed across nodes and the path lengths. (correct)
  • The emotional intensity of the nodes.
  • The historical contexts of the network nodes.
  • The geographical locations of the nodes.

According to the model described by the text, what does the probability '$p$' represent when creating random networks?

<p>The probability of any given link forming between two nodes. (A)</p> Signup and view all the answers

What does it mean to say that link formation is 'independent' across links in the model?

<p>The formation of one link has no influence on the formation of any other link. (C)</p> Signup and view all the answers

Who provided seminal studies of random networks as described in the text?

<p>Erdös and Rényi. (C)</p> Signup and view all the answers

Which of the following is a key goal of comparing observed networks with random networks?

<p>To identify elements of social structure that are not due to randomness. (C)</p> Signup and view all the answers

Which scenario is considered in the models alongside the probability model described in the text?

<p>A precise number of links being formed from all possible links. (D)</p> Signup and view all the answers

In the context of network analysis, what does P(ij) represent?

<p>The number of shortest paths connecting family i to family j. (C)</p> Signup and view all the answers

What does Pk(ij) signify in the context of network paths?

<p>The number of shortest paths that family k lies on, connecting families i and j. (A)</p> Signup and view all the answers

If there are two shortest paths between families A and B, and family C is on one of them, what would be the value of P_C(AB)?

<p>1 (D)</p> Signup and view all the answers

How is the betweenness centrality measure calculated for a family?

<p>By averaging the fraction of shortest paths a family lies on, across all pairs of other families (A)</p> Signup and view all the answers

In the betweenness formula, what does the term (n-1)(n-2)/2 represent?

<p>The number of possible pairs of families between which a family could lie on a path. (D)</p> Signup and view all the answers

If a family lies on all shortest paths between two other families, what would be the fraction of paths that family lies on, for that particular pair?

<p>1 (A)</p> Signup and view all the answers

What would be the betweenness value of a family that is not on any shortest path between any two families?

<p>0 (A)</p> Signup and view all the answers

What is the betweenness measure of the Medici family?

<p>0.522 (A)</p> Signup and view all the answers

What does the betweenness measure of a family in the marriage network indicate?

<p>The proportion of shortest paths between other families that pass through the family. (D)</p> Signup and view all the answers

What was the betweenness centrality of the Strozzi family in the marriage network?

<p>.103 (B)</p> Signup and view all the answers

According to the analysis, what does the Medici family's high betweenness suggest about their position?

<p>They were optimally positioned for facilitating information flow and political decisions. (B)</p> Signup and view all the answers

What, besides circumstance, contributed to the Medici family's consolidation of power?

<p>Their strategic network position, spanning disjunctures among the elite. (D)</p> Signup and view all the answers

According to the provided figure, what is the total utility of the network with a line structure at time t=3?

<p>4 (A)</p> Signup and view all the answers

The analysis of the marriage network suggests that network structure is important for understanding the social dynamics, and that:

<p>Different measures of centrality capture different aspects of the network. (A)</p> Signup and view all the answers

What is a 'network disjuncture', as mentioned in the context of the Medici family?

<p>A gap or separation between different parts of the network. (C)</p> Signup and view all the answers

What is the primary focus of the models discussed in the text regarding network efficiency?

<p>Achieving high utility with specific network structures. (D)</p> Signup and view all the answers

What is a key characteristic of the efficient networks discussed in the context?

<p>They are either star, empty, or complete networks. (C)</p> Signup and view all the answers

What aspect of the marriage arrangements is highlighted by the text?

<p>They were planned solely by the patriarchs of the families. (C)</p> Signup and view all the answers

The analysis uses a subset of families to conduct the calculations. How does this affect the results?

<p>The results are similar to those found in other studies, but slightly different in numbers and not representative of all families in the historical data. (C)</p> Signup and view all the answers

What is the main factor that determines agent's utilities in the network models?

<p>Path length and decay with distance. (B)</p> Signup and view all the answers

What does the concept of 'pairwise stability' aim to capture in the study of networks?

<p>The notion that establishing links require both parties' mutual agreement. (B)</p> Signup and view all the answers

What condition would cause a link to be removed based upon the concept of pairwise stability?

<p>When one agent benefits by terminating the relationship. (A)</p> Signup and view all the answers

According to the pairwise stability concept, when is a link added between two agents?

<p>When both agents would benefit from adding the link. (D)</p> Signup and view all the answers

What is the meaning of network 'completeness' within the studied models?

<p>Each individual node is directly linked to every other node in the network. (B)</p> Signup and view all the answers

What does the factor between 0 and 1 signify in the context of network relationships?

<p>The benefit derived from a direct relationship, diminishing with distance (D)</p> Signup and view all the answers

In the connections model, what determines a player's net utility from a network?

<p>The sum of benefits from the player's connections, minus the cost of maintaining the player's links (B)</p> Signup and view all the answers

In the connections model, which factor is represented by d_i(g)?

<p>The number of direct links maintained by player <em>i</em> (D)</p> Signup and view all the answers

What is the impact of raising the benefit factor to higher powers in more distant relationships?

<p>It leads to a lower benefit from the indirect connection. (B)</p> Signup and view all the answers

What determines if a network is considered efficient?

<p>When the total utility of all players in the network is maximized (A)</p> Signup and view all the answers

In the context of network formation, what is the main difference between benefits and costs?

<p>Benefits are given for both direct and indirect links, whereas costs are only for direct relationships. (B)</p> Signup and view all the answers

What happens to the benefit factor as relationships become more distant?

<p>The benefit factor is raised to higher powers, decreasing the benefit. (B)</p> Signup and view all the answers

Considering self-interested players, what is the focus of the connections model?

<p>Understanding which networks are most efficient and likely to form when players choose their own links (C)</p> Signup and view all the answers

In a binomial model of link formation, what does the probability $p$ represent?

<p>The probability that a link will form between any two specific nodes. (A)</p> Signup and view all the answers

What does the term 'degree' of a node refer to in the context of network analysis?

<p>The number of links connected to that specific node. (B)</p> Signup and view all the answers

According to the formula provided, what is the probability of a specific network with $m$ links forming in a network of $n$ nodes?

<p>$p^m(1-p)^{n(n-1)/2 - m}$ (B)</p> Signup and view all the answers

What does the degree distribution of a random network describe?

<p>The probability that a node will have a certain number of links. (B)</p> Signup and view all the answers

What happens to the correlation of degree between any two nodes as n (the number of nodes) becomes large?

<p>It decreases and approaches zero, becoming negligible. (A)</p> Signup and view all the answers

In a binomial model with n = 3, what is the probability of forming a network with two links if the probability of link formation is p?

<p>$3p^2(1-p)$ (A)</p> Signup and view all the answers

In the context of the binomial model, the formula that describes the probability of a node having exactly d links is:

<p>$p^d(1-p)^{n-1-d}$ (C)</p> Signup and view all the answers

Consider a random network with 4 nodes. If the probability of a link forming is p, what is the probability of the 'empty network' forming (zero links)?

<p>$(1-p)^6$ (A)</p> Signup and view all the answers

Flashcards

Betweenness

A measure of how often a family is on the shortest paths between other families.

Shortest Path

The minimum number of links connecting two families in a network.

Path Count P(ij)

Number of shortest paths connecting family i to family j.

Pk(ij) Definition

The number of shortest paths between families i and j that family k lies on.

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Calculating Betweenness

Average the fraction of paths a family lies on across all pairs of families.

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Freeman's Measure

A specific betweenness calculation method by sociologist Linton Freeman.

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Power Measure

A way to assess a family's centrality in a network using betweenness.

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Network Structure

The arrangement and connections of families within a social network.

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Medici Family

An influential family in Florence known for their power, particularly in terms of betweenness in social networks.

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Political Control

The ability to influence or direct the political affairs of a region, often facilitated by social ties.

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Guadagni Family

The second highest family in terms of betweenness, known for their role in Florence's elite network.

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Centrality

A concept in network analysis that reflects the importance of a node in a network.

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Elite Marriages

Strategically arranged unions among powerful families to strengthen alliances and influence.

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Wasserman and Faust

Researchers who contributed to the analysis of social network structures and dynamics.

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Binomial Model

A model where link formation occurs with probability p independently.

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Probability of Complete Network

Probability that a complete network forms is p raised to the number of links.

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Degree of a Node

The degree of a node is the count of links it has.

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Degree Distribution

Describes the probability of a node having a specific degree d.

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Probability of d Links

Probability a node has exactly d links is calculated using binomial formula.

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Correlation of Degrees

Links are formed independently, but degree correlation exists initially.

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Effect of Large n

As n increases, correlation of degrees between nodes vanishes.

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Probability Formula for m Links

Probability of network with m links on n nodes follows a specific binomial distribution formula.

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Network Formation

The process by which connections or links are established between nodes in a network.

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Random Networks

Networks formed through a completely random process, where links between nodes are created without systematic rules.

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Erdös and Rényi Model

A foundational model of random networks where each link between n nodes is formed with a fixed probability p.

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Node

An individual element or point in a network, which can be connected to other nodes.

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Link

A connection between two nodes in a network, representing a relationship or interaction.

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Path Length

The number of links (or steps) required to travel from one node to another in a network.

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Isolated Nodes

Nodes in a network that have no connections or links to any other nodes.

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Benchmark

A standard or point of reference used for comparisons, particularly in assessing different network properties.

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Net Utility (ui)

The total benefit a player receives from connections minus their maintenance costs.

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Direct Connection Benefit

The immediate advantage a player gains from linking directly with another player.

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Indirect Connection Benefit

The advantage a player gains from links to others through a chain of connections.

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Link Maintenance Cost (c)

The cost players incur to keep their direct connections active.

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Degree of a Player (di)

The number of direct connections a player has in the network.

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Efficient Network Definition

A network that maximizes total utility for all players involved.

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Shortest Path ( `ij(g))

The fewest links connecting two players in the network.

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Benefit from Connections Formula

A formula to calculate net utility considering both direct and indirect benefits.

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Total Utility

The overall satisfaction gained from consuming goods or services.

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Star Network

A network structure where one central node connects to all other nodes.

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Pairwise Stability

A network condition where no agent can benefit by deleting a link, and no two agents can benefit by creating a new one.

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Efficient Networks

Networks that maximize utility while minimizing costs, usually depicted as stars, complete or empty.

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Link Deletion

The act of removing a connection between two nodes in a network.

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Link Addition

The process of forming a new connection between two agents in a network.

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Utility Decay

The decrease in satisfaction as distance or path length increases.

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Study Notes

Social and Economic Networks

  • This book, "Social and Economic Networks," by Matthew O. Jackson, is used in Mathematical Economics 2.
  • It introduces network analysis, showcasing research examples.
  • Social networks play a central role in information exchange, trade, disease transmission, and many other aspects of social and economic life.
  • Networks influence behavior, and understanding their structures is important.

Chapter 1 - Introduction

  • Networks are central to social and economic activities.
  • The chapter provides examples of network analysis.
  • Key aspects of network analysis include types of networks, methodologies, approaches, and subject relevance.

1.1 Why Model Networks?

  • Social networks affect economic and social life significantly.
  • Networks influence crucial elements like job opportunities, insurance, and disease spread.
  • Network structure greatly influences individual behavior and societal outcomes.

1.2 A Set of Examples

  • Florentine Marriages: This study details the role of Medici's network of family marriages and alliances in accumulating power.
  • High School Friendships: Analysis of social networks among high school students from the Add Health data set, illustrating homophily (similarity in choices) and network structure.

1.2.3 Random Graphs and Networks

  • Random graph models show how links form randomly in a network, providing a useful comparison for real-world networks.
  • In random networks with high numbers of links, the majority of nodes are part of the same cluster ("giant component").
  • Degree distribution analysis provides insights into the structure of random networks.
  • Random network models can be compared to real-world social and economic networks to identify differences.

Exercises

  • Various exercises focus on betweenness centralities, degree centrality in networks.
  • Exercises also explore random network generation and properties in more detail.

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