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Organizations and their effectiveness-2016/Key concept definitions
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== Network == === Dan W === '''Definition:''' A non-random set of meaningful relationships distributed among individuals (or organizations, or any other purposive entities) that together do not reduce to the aggregate properties of those connected individuals (Inspired by: Scott (1991) -- the one and only textbook on social networks anyone ever needs!). ''Important elements of my definition:'' - “non-random” - social relationships emerge between entities in a social environment for some articulable, and often observable, reason. - “meaningful” - a set of relationships that contributes interpretive richness to the entities connected by those relationships beyond their individual characteristics. - “purposive” - entities connected by network relationships have their own desires which are sometimes liberated and sometimes shackled depending on the pattern, strength, and nature of the networks in which they are embedded. ''Example:'' - What does a real network look like with real consequences? Padgett and McLean (2006) show that a centuries-long intermarriage network between families representing different guilds after the Ciompi revolt around the time of Renaissance Florence redefined the economic and social actions of those families, giving birth to the partnership system of economic organization === Romain === '''Definition:''' a network is a collection of nodes and a collection of ties among these nodes. Types of networks: Several common distinctions are often made when talking about networks. A network can be directed or undirected (tie from $i$ to $j \neq$ tie from $j$ to $i$), and weighted or unweighted. One can also consider static vs. dynamic networks (ties or nodes are created/disappear over time), or multiplex networks (there are several types of ties). When talking about networks, one should always define: (1) what type of network are we talking about, (2) what is a node, (3) what is a tie. Examples: friendship network [type = undirected, unweighted network, node = person, tie = $i$ and $j$ are friends], airport traffic [type = weighted, directed network, node = airport, tie = number of daily flights from airport $i$ to airport $j$] '''(Theoretical) network models:''' Two broad distinctions: (1) network formation vs. process on a network, (2) non-strategic [no game theory] vs. strategic [game theory]. Examples: Non-strategic game of network formation: Barabassi and Albert's model of preferential attachment. Question: Why do networks often exhibit a hub and spoke structure [few nodes with many connections, many nodes with few connections]? Model: start with one node. At each time period, a new node is created and forms 1 tie with some old node selected at random. Old nodes with more connections are selected with higher probability. Strategic game of network formation: Matt Jackson's coauthor's model. Question: how does a population of scholars pick coauthors? Authors choose whether to form ties with other authors. Two authors with a tie are coauthors. Players' utility increases with the number of coauthors, but busy coauthors (ie coauthors with many connections) give less benefits less than non-busy coauthors. Non-strategic process on a network: probabilistic diffusion model. Some disease diffuses on a network. Question: which structures lead to a pandemic (everybody is infected), which do not? On a network, an initial node is infected (the seed). She infects her neighbors with some probability. At each time period, newly infected nodes infect their neighbors with some probability. Strategic process on a network: Chwe's model of social movements. Question: which network structures lead to a revolution (every node protests)? On a network, each node has a threshold. A node protests if the number of her neighbors who protest is above that threshold.
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