Issue
EPL
Volume 85, Number 2, January 2009
Article Number 28001
Number of page(s) 6
Section Interdisciplinary Physics and Related Areas of Science and Technology
DOI http://dx.doi.org/10.1209/0295-5075/85/28001
Published online 29 January 2009
EPL, 85 (2009) 28001
DOI: 10.1209/0295-5075/85/28001

Sampling bias in systems with structural heterogeneity and limited internal diffusion

J.-P. Onnela1, 2, 3, N. F. Johnson4, S. Gourley1, 2, G. Reinert5 and M. Spagat6

1   Department of Physics, University of Oxford - Oxford OX1 3PU, UK, EU
2   CABDyN Research Cluster, Said Business School, University of Oxford - Oxford, OX1 1HP, UK, EU
3   DBEC, Helsinki University of Technology - P.O. Box 9203, Helsinki, FIN-02015 HUT, Finland, EU
4   Physics Department, University of Miami - Coral Gables, FL 33124, USA
5   Department of Statistics, University of Oxford - Oxford OX1 3TG, UK, EU
6   Department of Economics, Royal Holloway, University of London - London, TW20 0EX, UK, EU

jp.onnela@physics.ox.ac.uk

received 13 October 2008; accepted in final form 22 December 2008; published January 2009
published online 29 January 2009

Abstract
Complex-systems research is becomingly increasingly data-driven, particularly in the social and biological domains. Many of the systems from which sample data are collected feature structural heterogeneity at the mesoscopic scale (i.e. communities) and limited inter-community diffusion. Here we show that the interplay between these two features can yield a significant bias in the global characteristics inferred from the data. We present a general framework to quantify this bias, and derive an explicit corrective factor for a wide class of systems. Applying our analysis to a recent high-profile survey of conflict mortality in Iraq suggests a significant overestimate of deaths.

PACS
89.65.-s - Social and economic systems.
89.75.Fb - Structures and organization in complex systems.
89.75.-k - Complex systems.

© EPLA 2009