Hookah use was assessed at 24 months by two items: (a) Have you ever tried a hookah? selleck (or water pipe; responses: yes or no) and (b) During the past days, on how many days did you smoke a hookah? (responses: 0, 1�C2, 3�C5, 6�C9, 10�C19, 20�C29, and all 30 days). Participants were also asked if they had ever been to a hookah bar, lounge, or restaurant (responses: yes/no) at the 24-month assessment. Smoking-related variables used in this study included current cigarette, smokeless tobacco, cigar (including cigarillos and little cigars), bidi (defined as sweet-flavored cigarettes from India), and kretek use (defined as clove-flavored cigarettes). Though these smoking-related variables were assessed at each wave, data from the 24-month assessment were used in this study.

Cigarette smoking was assessed by items that asked about participants�� number of days smoked in the past thirty days (responses: 0, 1�C2, 3�C5, 6�C9, 10�C19, 20�C29, and all 30 days) and the number of cigarettes smoked each day during the past thirty days. Smokeless tobacco, cigar, bidi, and kretek use were each assessed by an item that asked about the number of days participants�� smoked the product in the past thirty days. Response categories for each of these items were 0, 1�C2, 3�C5, 6�C9, 10�C19, 20�C29, and all 30 days. School performance was assessed by asking participants, ��Which of the following best describes your average grade in school this year?�� (responses: A+, A?, B+, B, B?, C+, C, C?, and D).

Substance use behaviors were assessed by asking participants the following: ��During the past three months how often Drug_discovery did you drink alcohol (beer wine, or wine coolers, liquor such as rum, gin, vodka or whiskey)?�� and ��During the past three months, how often did you smoke marijuana (grass, pot, weed, sins, buds, or hash)?�� Responses for each item were zero times, once a month or less, more than once a month but less than once a week, one or more times a week but not every day, and every day. Statistical Analysis Participant demographics, smoking-related and substance use behaviors, and school performance variables were explored using descriptive statistics. To assess the prevalence of hookah use among adolescents in our sample, we conducted descriptive analyses, comparing questionnaire responses from those participants who reported ever and current hookah use (or 30-day users, defined as using a hookah at least once in the past thirty days prior to the survey) at 24 months and those that did not report use. The prevalence of multiple tobacco product use among hookah smokers and nonusers was also assessed. To account for clustering within schools, models with school as cluster were run using the SAS Proc GLIMMIX procedure.