strengths are enforced. Our findings complement the existing economic literature on (dynamic) intensive and extensive trade margins. More in general, they show that real-world multiplexes can be strongly shaped by layer-specific local constraints.'
author:
- Rossana Mastrandrea
- Tiziano Squartini
- Giorgio Fagiolo
- Diego Garlaschelli
bibliography:
- 'resubmitted2PRE.bib'
title: |
    Reconstructing the world trade multiplex:\
    the role of intensive and extensive biases
---

Introduction
============

Over the last fifteen years, there has been a dramatic rise of interest towards the mechanisms of network formation [@AlbertBarabasi2002; @Jackson03survey]. One of the reasons lies in the fact that the dynamics of a wide range of important phenomena (e.g. disease spreading and information diffusion) is strongly affected by the topology of the underlying network mediating the interactions. Economic networks are particularly relevant for the emergence of many processes of societal relevance such as globalization, economic integration, and financial contagion [@ScienceNets2009].

In order to identify the non-trivial structural properties of a real network, one needs to appropriately define and implement a *null model*. Comparing a real network with a null model allows one to reveal statistically significant structural patterns. Substantial effort has been devoted to the definition of null models for graphs [@Katz_Powell_1957; @Erdos_Renyi_1960; 