Core–periphery structure: Difference between revisions

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{{Short description|Network theory model}}

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[[File:Core-Periphery Network.png|thumb|A Network with an idealized core–periphery structure]]

'''Core–periphery structure''' is a [[network theory]] model.

'''Core–periphery structures''' are commonly found in [[Economics of networks|economic]] and [[social network]]s. They consist of a dense cohesive core and a sparse, loosely connected periphery. (Zhang, Martin, & Newman, n.d.) Networks can be described from various macro, micro and meso scales. Identifying these structures allows for the comparison between complex structures. (Rombach, Porter, Fowler, & Mucha, 2014)

[[File:Core-Periphery Network.png|thumb|A Network with an idealized core–periphery structure]]

==Models of core–periphery structures==

There are two main intuitions behind the definition of core–periphery network structures; one assumes that a network can only have one core, whereas the other allows for the possibility of multiple cores. These two intuitive conceptions serve as the basis for two modes of core–periphery structures.

===Discrete model===

This model assumes that there are two classes of nodes. The first consists of a cohesive core sub-graph in which the nodes are highly interconnected, and the second is made up of a peripheral set of nodes that is loosely connected to the core. In an ideal core–periphery matrix, core nodes are adjacent to other core nodes and to some peripheral nodes while peripheral nodes are not connected with other peripheral nodes (Borgatti & Everett, 2000, p. 378). This requires, however, that there be an a priori partition that indicates whether a node belongs to the core or to the periphery.

[[File:Core-Periphery Matrix.png|thumb|In this idealized matrix, the blue block represents core-core links, the white block represents the absence of periphery–peripheryperiphery links and the red quadrants represent core–periphery ties.]]

===Continuous model===

This model allows for the existence of three or more partitions of node classes. However, including more classes makes modifications to the discrete model more difficult.{{clarify|date=August 2019}} Borgatti & Everett (20001999) suggest that, in order to overcome this problem, each node be assigned a measure of ‘coreness’ that will determine its class. Nevertheless, the threshold of what constitutes a high ‘coreness’ value must be justified theoretically.

==Discussion==

Hubs are commonly found in [[empirical networks]] and pose a problem for community detection as they usually have strong ties to many communities. Identifying core–periphery structures can help circumvent this problem by categorizing hubs as part of the network’snetwork's core. (Rombach et al., 2014, p. 160). Likewise, though all core nodes have high centrality measures, not all nodes with high centrality measures belong to the core. It is possible to find that a set of highly central nodes in a graph does not make an internally cohesive subgraph. (Borgatti & Everett, 2000)...

==Uses in economics==

The concept ofwas centerfirst andintroduced peripheryinto waseconomics firstas introduced"centre-periphery" by [[Raúl Prebisch]] in the 1950s. However, but the qualitativeorigin notionof thatthe socialidea networkscould canultimately havebe atraced core–peripheryback structureto has[[Johann aHeinrich longvon historyThünen|Thünen]]'s in''Isolated disciplinesState'' such(1826).<ref>{{Cite asjournal sociology,|last1=Rama international|first1=J. relations|last2=Hall (Nemeth|first2=J. &|year=2021 Smith,|title=Raúl 1985),Prebisch and economicsthe (Snyderevolving &uses Kick,of 1979).'centre-periphery'in economic analysis |journal=Review of Evolutionary Political Economy |volume=2 |issue=2 |pages=315–332}}</ref> Observed trade flows and diplomatic ties among countries fit this structure. [[Paul Krugman]] (1991) suggests that when transportation costs are low enough manufacturers concentrate in a single region known as the core and other regions (the periphery) limit themselves to the supply of agricultural goods.

==See also==

*[[World-systems theory]]

*[[Core countries]]

*[[Semi-periphery countries]]

*[[Periphery countries]]

*[[Degeneracy (graph theory)]]

==References==

{{reflist}}

* [[Stephen Borgatti|Borgatti, S. P.]], & Everett, M. G. (20001999). Models of core /periphery structures. Social Networks, 21, 375–395. doi:10.1016/S0378-8733(99)00019-2

* Borgatti, S. P., & Everett, M. G. (2000). Models of core /periphery structures. Social Networks, 21, 375–395. doi:10.1016/S0378-8733(99)00019-2

* Krugman, P.R. (1991), Increasing returns and economic geography, Journal of Political Economy 99, 483–499.

* Nemeth, R. J., & Smith, D. A. (1985). International trade and world-system structure: A multiple network analysis (No. 8).

* Rombach, M. P., Porter, M. A., Fowler, J. H., & Mucha, P. J. (2014). Core–periphery structure in Networks. SiamSIAM J. Appl. Math., 74(1), 167–190.

* Snyder, D., & Kick, E. L. (1979). Structural position in the world system and economic growth, 1955–1970: A multiple-network analysis of transnational interactions. American Journal of Sociology, 84, 1096–1126.

* Wallerstein, I. (1978). World-system analysis: theoretical and interpretative issues. ''World-System Analysis: Theory and Methodology'', 91-103.

* Zhang, X., Martin, T., & Newman, M. E. J. (n.d.). Identification of core–periphery structure in networks, 1–10.

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[[Category:Network theory]]