title: Reconstructing the world trade multiplex: the role of intensive and extensive biases.
abstract: In economic and financial networks, the strength of each node has always an important economic meaning, such as the size of supply and demand, import and export, or financial exposure. Constructing null models of networks matching the observed strengths of all nodes is crucial in order to either detect interesting deviations of an empirical network from economically meaningful benchmarks or reconstruct the most likely structure of an economic network when the latter is unknown. However, several studies have proved that real economic networks and multiplexes topologically differ from configurations inferred only from node strengths. Here we provide a detailed analysis of the world trade multiplex by comparing it to an enhanced null model that simultaneously reproduces the strength and the degree of each node. We study several temporal snapshots and almost 100 layers (commodity classes) of the multiplex and find that the observed properties are systematically well reproduced by our model. Our formalism allows us to introduce the (static) concept of extensive and intensive bias, defined as a measurable tendency of the network to prefer either the formation of extra links or the reinforcement of link weights, with respect to a reference case where only strengths are enforced. Our findings complement the existing economic literature on (dynamic) intensive and extensive trade margins. More generally, they show that real-world multiplexes can be strongly shaped by layer-specific local constraints.
authors.affiliation: Institute of Economics and LEM, Scuola Superiore Sant'Anna, 56127 Pisa, Italy and Aix Marseille Université, Université de Toulon, CNRS, CPT, UMR 7332, 13288 Marseille, France.
authors.forename: Rossana
authors.initials: R
authors.lastname: Mastrandrea
authors.affiliation: Instituut-Lorentz for Theoretical Physics, University of Leiden, 2333 CA Leiden, The Netherlands and Institute for Complex Systems UOS Sapienza, "Sapienza" University of Rome, P.le Aldo Moro 5, 00185 Rome, Italy.
authors.forename: Tiziano
authors.initials: T
authors.lastname: Squartini
authors.affiliation: Institute of Economics and LEM, Scuola Superiore Sant'Anna, 56127 Pisa, Italy.
authors.forename: Giorgio
authors.initials: G
authors.lastname: Fagiolo
authors.affiliation: Instituut-Lorentz for Theoretical Physics, University of Leiden, 2333 CA Leiden, The Netherlands.
authors.forename: Diego
authors.initials: D
authors.lastname: Garlaschelli