However, the study also has several limitations. Self-reported measures are susceptible to memory bias and the social desirability effect. Events that are salient and recent are more likely to be remembered and reported than those that are less salient and more distant. The measures for antismoking interventions did not assess the intensity of events, only whether or not they occurred, and this cell differentiation may have contributed to the lack of effect. The use of cross-sectional data also precludes any inferences about the directionality of effects. Thus, it is possible that adolescents who are more interested in smoking may be the ones who are more likely to report noticing antismoking messages or receiving antismoking education or advice.

Conclusions Educating adolescents about the danger of smoking in schools is an effective means of reducing their smoking susceptibility in Malaysia and Thailand, although different prevention strategies may be necessary to ensure effectiveness for male and female adolescents. Nation-wide antismoking media campaign may be another important means of communicating the risk of smoking to adolescents. Funding The ITC-SEA Project is supported by grants P50 CA111236 (Roswell Park Transdisciplinary Tobacco Use Research Center), R01 CA100362 (National Cancer Institute of the United States), 79551 (Canadian Institutes of Health Research), Ontario Institute for Cancer Research, ThaiHealth Promotion Foundation, and the Malaysian Ministry of Health. Declaration of Interests None declared. Acknowledgments Special thanks to A. S. Mohd Samin and the data collection team, N.

A. Abd Rani, S. H. Zyoud, and Dr. Anne C. K. Quah, for their assistance toward the success of this article. The authors acknowledge the Universiti Sains Malaysia for the fellowship provided to S. Zawahir. We would also like to acknowledge the other members of the ITC Project team.
To enhance the effectiveness of youth substance use prevention GSK-3 programs, most of which have a strong focus on peers (see for example, Campbell et al., 2008 and D��Amico & Edelen, 2007), it is imperative to understand the nexus of substance use-related peer influence. Cross-sectional and prospective studies have shown that exposure to prosmoking peer behaviors and attitudes is associated with the initiation and escalation of smoking use during adolescence (Flay, Hu, & Richardson, 1998; Griffin, Botvin, Doyle, Diaz, & Epstein, 1999; Peterson et al., 2006; Tucker, Ellickson, & Klein, 2002, 2003; Wang et al., 1999). Studies reporting a correlation between the smoking behavior of adolescents and their peers typically conclude that this association is due to adolescents being influenced by their friends.