School weights were calculated by multiplying number of schools selleck products selected from each stratum with the probability of selecting a particular school and taking the inverse of the result. Weighted analyses were performed using ��Complex Samples�� procedure in SPSS, which takes into account both the stratification and the clustering of the sample when calculating the confidence intervals around the estimates. Statistical analysis was performed using SPSS v. 19.0 (SPSS Inc, Chicago, IL). Results Of the 1,781 students enrolled at baseline, 1,701 (95.5%) were still in the study and completed the 2-year follow-up survey (869 boys, median age at baseline 13 years). Prevalence of ever and current cigarette smoking was considerably higher in boys than girls both at baseline and follow up (p < .

01 for all comparisons). The same findings were observed for water-pipe smoking although the differences between boys and girls were smaller than those of cigarette smoking for both ever and current WP smoking (p < .01 for all comparisons; Table 1). Table 1. Change in Prevalence of Indicators of Tobacco Smoking Between Seventh Grade (Baseline, Mean Age 13) and Ninth Grade in Northern Jordan, by Gender Ever smoking any kind (cigarette and/or water pipe) was reported by 31.4% of students at baseline and increased to 55.2% 2 years later, while current smoking any kind was reported by 15.2% of students at baseline and increased to 25.0% 2 years later (Table 1). Time Trends in Cigarette Smoking Overall, ever cigarette smoking increased 2.5 times during the 2-year follow-up period (from 17.6% to 44.

7%; p < .01), while current cigarette smoking almost tripled during the same period (from 5.3% to 14.9%; p < .01). When analyzed by gender, similar trends were observed in both sexes (Table 1). For never smokers at baseline, among the 643 boys, 227 (35.3%) became ever smokers 2 years later��of which 95 (14.8%) were current and 40 (6.2%) were daily smokers. While among the 759 never-smoker girls, 143 (18.8%) became ever smokers 2 years later��of which 32 (4.2%) were current and 5 (0.7%) were daily smokers (Table 2). Table 2. Smoking Patterns at 2-Year Follow-up Among Never Smokers at Baseline, by Gender Time Trends in Water-Pipe Smoking The change over time for water-pipe smoking was less prominent than that of cigarette smoking. Prevalence of ever water-pipe smoking increased 1.

8 times during the 2-year follow-up period (from 25.9% to 46.4%; p < .01), while current water-pipe smoking increased 1.4 times during the Brefeldin_A same period (from 13.3% to 18.9%; p < .01). Similar to finding from cigarette smoking, change of water-pipe smoking over time was essentially similar in boys and girls��both for ever and current water-pipe smoking (Table 1). For never smokers at baseline, among the 564 boys, 196 (33.0%) became ever smokers 2 years later��of which 85 (15.1%) were current and 12 (2.1%) were daily smoker (Table 3).