“A longitudinal social network analysis of peer influence, peer selection and smoking behaviour among adolescents in British schools.”
By Liesbeth Mercken, Philip Sinclair, Christian Steglich, Jo Holliday, and Laurence Moore, 2011.
Health Psychology, January 16, 2012.

Objective: Similarity in smoking behaviour among adolescent friends could be caused by selection of friends on the basis of behavioural similarity, or by influence processes, where behaviour is changed to be similar to that of friends. The main aim of the present study is to disentangle selection and influence processes and study changes over time in these processes using new methods of longitudinal social network analysis. Methods: The sample consists of 1716 adolescents (mean age at baseline=12.17, SD=.38) in 11 British schools participating in the control group of the ASSIST (A Stop Smoking in School Trial) study. The design was longitudinal with three observations at one year intervals. At each observation, participants were asked to report on their smoking behaviour and friendship networks. An actor-based model of friendship network and smoking behaviour co-evolution (a statistical model for the simultaneously occurring changes in friendship nominations and smoking) was analysed, capable of modelling possible changes occurring between observations, allowing alternative influence and selection mechanisms to be investigated, and avoiding the violation of assumptions of statistical independence of observed data. Results: Adolescent's tendency to select friends based on similar smoking behaviour was found to be a stronger predictor of smoking behaviour than friends' influence. The proportion of smoking behaviour similarity explained by smoking-based selection of friends increased over time, whereas the proportion explained by influence of friends decreased. Conclusions: Smoking prevention should not solely focus on social influence, but also consider selection processes and changes in both processes over time during adolescence.

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