Ricerc@Sapienza

In this work, we develop the Tsallis entropy approach for examining the 1
cross-shareholding network of companies traded on the Italian stock market. In such a network, 2
the nodes represent the companies, and the links represent the ownership. Within this context, we 3
introduce the out-degree of the nodes – which represents the diversification – and the in-degree 4
of them – capturing the integration. Diversification and integration allow a clear description 5
of the industrial structure formed by the considered companies. The stochastic dependence of 6
diversification and integration is modelled through copulas. We argue that copulas are well suited 7
for modelling the joint distribution. The analysis of the stochastic dependence between integration 8
and diversification by means of the Tsallis entropy gives a crucial information on the reaction of 9
the market structure to the external shocks, - on the basis of some relevant cases of dependence 10
between the considered variables. Indeed, the considered entropy framework provides insights on 11
the relationship between in-degree and out-degree dependence structure and market polarisation or 12
fairness. Moreover, the interpretation of the results in the light of the Tsallis entropy parameter gives 13
relevant suggestions for policymakers who aim at shaping the industrial context for having high 14
polarisation or fair joint distribution of diversification and integration. Furthermore, a discussion 15
of possible parametrisations of the in-degree and out-degree marginal distribution, – by means of 16
power laws or exponential functions, – is also carried out. An empirical experiment on a large 17
dataset of Italian companies validates the theoretical framework.