This cross-sectional study was confirmed by the Ethics Committee of Shahed University, Tehran, Iran. It was conducted in accordance with the ethical standards of the Declaration of Helsinki (1975, revised in 1983) among university students in Tehran. The institutions were four major universities including Shahed University, Tehran University, Azad University and Art University. The sample size used in descriptive study was calculated by a pilot study through the following formula. When the estimated prevalence (P) is, precision error estimation (d) is 0.04, and alpha (α) is 0.05), the sample size became 384 cases. A sample of 400 participants was obtained from each university by a two-stage cluster sampling. Four major universities in Tehran were selected from which 400 participants were chosen by random sampling generated in Microsoft Excel 2007. The data were collected between April and May 2010.
Each student attended morning classes of at least one semester was included in this study. Exclusion criteria were incomplete questionnaires as well as unwillingness to answer questions. An anonymous questionnaire with 46 questions was administered. The draft of the questionnaire was composed for the focus group and refined through validation process. Content and face validity of the questionnaire were evaluated by a panel of experts. To this end, a number of specialists and experts were invited to participate in assessing the validity of the questionnaire. Thereafter, the questionnaire was corrected according to the feedback. A pilot study on a group of 100 participants was conducted to verify the reliability of the questionnaire; Cronbach's alpha value was obtained as 0.76. The first section of the questionnaire was designed to explore the socio-demographic details (22 questions). In the second section, a questionnaire for the purpose of smoking status was conducted (23 questions). In the closing section, one question was asked about the degree of attention they paid to completing the questionnaire. Only smokers had to fill in all the 23 questions related to smoking. The students were visited at their classrooms. Notably, they were informed of the study's purpose both verbally and in writing. Then, they were asked to complete the questionnaire under the supervision of the researchers. None of the students present in the classrooms during the visit refused to answer the questionnaire.
Descriptive statistics including frequency distribution tables and mean ± standard deviations (SD) were generated with SPSS, version 17 (Chicago, Illinois, USA). A chi-square or Fisher’s exact test was used to compare categorical variables. An independent t-test or Mann-Whitney test was used to compare the means. The significant level was defined as P < 0.05.