The study aim should be more precise "The aim of this study was...." Response 1.
lack of analysis of second-hand smoke exposure. Specifically, whether exposure increases risk of smoking. Correlations do not confirm causality. It is likely that students who smoke actively seek roommates who smoke, and students who do not smoke seek roommates who do not smoke. Thus, exposure alone offers little information about the role of second-hand smoke and "contagion."