Can we neglect the multi-layer structure of functional networks?

TL;DR

This paper investigates whether simplifying multi-layer functional networks into single-layer projections affects our understanding, using European airport delay networks as a case study, and finds that neglecting the multi-layer structure can lead to significant misunderstandings.

Contribution

The study demonstrates the importance of considering multi-layer structures in functional networks, highlighting potential misinterpretations when using simplified single-layer projections.

Findings

Neglecting multi-layer structure impacts understanding of delay propagation.

Single-layer projections can misrepresent the system dynamics.

Multi-layer analysis provides more accurate insights into complex systems.

Abstract

Functional networks, i.e. networks representing dynamic relationships between the components of a complex system, have been instrumental for our understanding of, among others, the human brain. Due to limited data availability, the multi-layer nature of numerous functional networks has hitherto been neglected, and nodes are endowed with a single type of links even when multiple relationships coexist at different physical levels. A relevant problem is the assessment of the benefits yielded by studying a multi-layer functional network, against the simplicity guaranteed by the reconstruction and use of the corresponding single layer projection. Here, I tackle this issue by using as a test case, the functional network representing the dynamics of delay propagation through European airports. Neglecting the multi-layer structure of a functional network has dramatic consequences on our understanding of the underlying system, a fact to be taken into account when a projection is the only available information.