Abstract
Objectives
The project aims to: (1) investigate structural and functional changes in an Australian drug trafficking network across time to determine ways in which such networks form and evolve. To meet this aim, the project will answer the following research questions: (1) What social structural changes occur in drug trafficking networks across time? (2) How are these structural changes related to roles/tasks performed by network members? (3) What social processes can account for change over time in drug trafficking networks?
Method
The relational data on the network was divided into four two years periods. Actors were allocated to specific roles. We applied a stochastic actor-oriented model to explain the dynamics of the network across time. Using RSiena, we estimated a number of models with the key objectives of investigating: (1) the effect of roles only; (2) the endogenous effect of degree-based popularity (Matthew effect); (3) the endogenous effect of balancing connectivity with exposure (preference for indirect rather than direct connections); (4) how degree-based popularity is moderated by tendencies towards reach and exposure.
Results
Preferential attachment is completely moderated by a preference for having indirect ties, meaning that centralization is a result of actors preferring indirect connections to many others and not because of a preference for connecting to popular actors. Locally, actors seek cohesive relationships through triadic closure.
Conclusions
Actors do not seek to create an efficient network that is highly centralized at the expense of security. Rather, actors strive to optimize security through triadic closure, building trust, and protecting themselves and actors in close proximity through the use of brokers that offer access to the rest of the network.
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Notes
Roles included resource provider, labourer, cook, manager, dealer, security, corrupt official.
A number of longitudinal models for networks have been proposed. We chose here a continuous-time framework rather than the discrete-time model proposed in Robins and Pattison (2001) and elaborated in Krackhardt and Handcock (2007) and Hanneke and Xing (2007). Snijders et al. (2010) discuss the principled differences between modelling tie-change in continuous- and discrete-time. This is further elaborated in Block et al. (2018). Furthermore, we chose an actor-oriented framework over a tie-based model. Block et al. (2017) provide a thorough comparison and a number of clarifications as to the differences and similarities between tie-based and actor-based models.
Currently missing ties at the start of a period are treated in a close approximation to this scheme. See further in Ripley et al. 2017. For the first observation Krause et al. (2017) follow Koskinen et al. (2015) and assume an exponential random graph for the ties in order to account for missings. Missingness in subsequent observations is handled using multiple imputation and not, as here, treated in a fully Bayesian way.
Jaccard indices are used to measure the amount of change from one network panel to the next. Higher values are indicative of greater stability.
Referred to as “Dyadic mechanisms” in the sequel.
Referred to as “Endogenous dynamics” in the sequel.
The results of Model 5 remain largely unchanged when an effect is added for the ‘popularity’ of the focal actors, suggesting that the other effects are robust to the centrality of the individuals whose cases-filed data were extracted from.
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Acknowledgements
Johan Koskinen's work was supported by Leverhulme Trust (RPG-2013-140) and BA/Leverhulme SRG 2012.
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Bright, D., Koskinen, J. & Malm, A. Illicit Network Dynamics: The Formation and Evolution of a Drug Trafficking Network. J Quant Criminol 35, 237–258 (2019). https://doi.org/10.1007/s10940-018-9379-8
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DOI: https://doi.org/10.1007/s10940-018-9379-8