  In this article we study the organizational structure of a large group of
members of the Sicilian Mafia by means of social network analysis and an
econometric analysis of link formation. Our mains results are the following. i)
The Mafia network is a small-world network adjusted by its criminal nature, and
is strongly disassortative. ii) Mafia bosses are not always central in the
network. In particular, consistent with a prediction of Baccara and Bar-Isaac,
we identify a "cell-dominated hierarchy" in the network: a key member is not
central, but is connected to a relative with a central position. iii) The
probability of link formation between two agents is higher if the two agents
belong to the same Mandamento, if they share a high number of similar tasks,
while being a "boss" reduces the probability of link formation between them.
iv) The probability of link formation for an individual agent is higher if he
is in charge of keeping connections outside his Mandamento, of collecting
protection money and or having a directive role, while age has modest role.
These results are interpreted in the light of the efficiency/security trade-off
faced by the Mafia and of its known hierarchical structure.
