title: Preferential attachment and growth dynamics in complex systems.
abstract: Complex systems can be characterized by classes of equivalency of their elements defined according to system specific rules. We propose a generalized preferential attachment model to describe the class size distribution. The model postulates preferential growth of the existing classes and the steady influx of new classes. According to the model, the distribution changes from a pure exponential form for zero influx of new classes to a power law with an exponential cut-off form when the influx of new classes is substantial. Predictions of the model are tested through the analysis of a unique industrial database, which covers both elementary units (products) and classes (markets, firms) in a given industry (pharmaceuticals), covering the entire size distribution. The model's predictions are in good agreement with the data. The paper sheds light on the emergence of the exponent tau approximately 2 observed as a universal feature of many biological, social and economic problems.
authors.affiliation: Center for Polymer Studies and Department of Physics, Boston University, Boston, Massachusetts 02215, USA.
authors.forename: Kazuko
authors.initials: K
authors.lastname: Yamasaki
authors.forename: Kaushik
authors.initials: K
authors.lastname: Matia
authors.forename: Sergey V
authors.initials: SV
authors.lastname: Buldyrev
authors.forename: Dongfeng
authors.initials: D
authors.lastname: Fu
authors.forename: Fabio
authors.initials: F
authors.lastname: Pammolli
authors.forename: Massimo
authors.initials: M
authors.lastname: Riccaboni
authors.forename: H Eugene
authors.initials: HE
authors.lastname: Stanley