Table 1.

Eligibility criteria using the PECO format

Criterion	Definition
(P) Population	• Secondary school students (age 11–18) • Focused on whole population or students of a low socioeconomic status • Papers published from 1997 onwards, using data from 1997 onwards • Papers with abstracts written in English
(E) Exposure	• Network characteristics (number of ties, network structure, betweenness and degree centrality, density) • Any study conducting cross-sectional or longitudinal network analysis
(C) Comparator	• Not applicable
(O) Outcome	• Link between network characteristics and smoking behaviour and attitudes • Network characteristics • Smoking prevalence