Hierarchy, Tasks, Space : an analysis of tie formation in the Palermo Mafia

We apply social network analysis to study tie formation among a large group of members of the Sicilian Mafia, one of the oldest criminal organizations, operating in the province of Palermo. Data come from the police operation denoted “Perseo”, which led to the arrest of 99 individuals active in the period 2006–2008. Specifically, we focus on the effect of hierarchical structure, task specialization patterns, and geographical organization on the probability of tie formation by estimating dyadic regressions. We find: First, if both agents in a dyad are bosses, two effects of opposite sign are at work: a scale effect, that increases the probability, and a homophily effect, that decreases such probability. Second, organizational task homophily positively affects tie formation, while criminal task homophily does not. Third, the key geographical variable driving tie formation is joint membership to the same mandamento, which makes sheer geographical distance non-statistically significant. We corroborate our results with several robustness tests and discuss their implications for an understanding of criminal organizations, such as the Cosa Nostra.