  The Eurovision Song Contest is a popular TV singing competition held annually
among country members of the European Broadcasting Union. In this competition,
each member can be both contestant and jury, as it can participate with a song
and/or vote for other countries' tunes. Throughout the years, the voting system
has repeatedly been accused of being biased by the presence of tactical voting,
according to which votes would represent strategic interests rather than actual
musical preferences of the voting countries. In this work, we develop a latent
space model to investigate the presence of a latent structure underlying the
exchange of votes. Focusing on the period from 1998 to 2015, we represent the
vote exchange as a multivariate network: each edition is a network, where
countries are the nodes and two countries are linked by an edge if one voted
for the other. The different networks are taken to be independent replicates of
a common latent space capturing the overall relationships among the countries.
Proximity denotes similarity, and countries close in the latent space are
assumed to be more likely to exchange votes. Therefore, if the exchange of
votes depends on the similarity between countries, the quality of the competing
songs might not be a relevant factor in the determination of the voting
preferences, and this would suggest the presence of bias. A Bayesian
hierarchical modelling approach is employed to model the probability of a
connection between any two countries as a function of their distance in the
latent space, and of network-specific parameters and edge-specific covariates.
The inferred latent space is found to be relevant in the determination of edge
probabilities, however, the positions of the countries in such space only
partially correspond to their actual geographical positions.

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