Dr Carl Phillips gives a fascinating presentation at City Health 2012 on tobacco harm reduction (THR) and illustrates with a complex systems model how THR will spread most readily in a dense urban population. It’s probably best to watch this video in the highest resolution you can, to best see the modelling. Carl’s blog about the talk is here
http://ep-ology.blogspot.com/2012/10/agent-based-model-of-thr-adoption-and.html