Cigarette Smoking and Its Risk Factors - NCBI

Cigarette Smoking and Its Risk Factors among Elementary School Students in Beijng

Bao-Pinig ZIti, MD, PhD, Minig Liii, MD, MS, Da,ia S/eltoni, MPH, Simmis Lila, MD, MS, and Gary A. Giovino, PhD, MS

Introduction Much of our current knowledge on teenage smoking has comc from Westcrn countries. Studies from these countries show that most smokers start smoking during their adolescent or early adulthood years'-3 and that the younger persons are when they start to smoke, the more likely they are to become regular smokers as adults. '3 In addition. persons w\ho start to smoke as young adolescents are among the heaviest tobacco users during adolescence and adulthood' and thus experience higher mortality from smoking-related diseases. '-'- Therefore, researchers in industrialized countries have repecatedly stressed the importance of preventing tobacco use among young people.' In Third World countries, however, smoking among children has not received as much attention. In China, a few studies have been conducted on smoking prevalence among adults. >8 To the best of our knowledge, however, no populationbased data are currently available on smoking behavior among children. Since more than one fifth of the world's population and more than 300 million (approximately 30%c) of the world's smokers live in China,9"1' the success in achieving global objectives in terms of smoking control as wcll as hcalth promotion largelx dcpends on how much progress in tobacco control is made in that country. Therefore. accurate documentation of the prevalence of smoking among children and adolescents in China, as well as its related behavioral patterns and risk factors. would benefit not only China but the entire world. To provide such estimates. we surveyed a stratificd random sample of 16 996 clementary school studcnts in Beijing during 1988. After reviwincg the literature. wc believe that this is onc of the largest

and most comprehensive studies ever conducted on smoking among children of this agce.

Methods Sample In China, the school system is uniform across the country. Childrcn typicallv cnter elcmentary school at the acle of 7 vears and graduatc at the agc of 12 ycars. The law requircs all childrcn to complcte elemcntary school. Thus. elcmentary school students virtually constitutc the cntire population bctvccn the aces of 7 acnd 12 vcars. We recruited only childrcn in oradcs 4 to 6. agcd mostly 10 to 12 years, bccausc this studv involved a self-administered questionnairc that required the rcspondcnts to bc of a substantial litcracyc level.

Bao-Pinc Zhu is wvith the Center for Public Health Research and Evaluation. Battclle Memorial Institute. Atlanta. Ga: the Office on Smoking and Health. National Center for Chronic Disease Prevention and Healthl Promotion. Atlanta: and the Div-ision of Social Medicine and Public Health. Chinese Academv of Medical Sciences and Peking Union Medical College. Beijing. China. Ming Liu is with the Division of Social Medicine and Public Health. Chinese Academy of Medical Sciences and Peking Union Medical College. and the Department of Internal Medicine. University of Michigan Medical Center. Ann Arbor. Dana Shelton and GarN A. Giovino are wN ith the Office on Smoking and Health, and Simin Liu is with the Division of Nutrition. National Center for Chronic Disease Prevention and Health Promotion. Requests for reprints should be sent to Bao-Ping Zhu. MD. PhD. Office on Smoking and Health. National Center for Chronic Disease Prevention and Health Promotion. Centers for Disease Control and Prevention. Mailstop K-5O. 47711 Buford Hwy NE. Atlanta. GA 30341-3724. This paper was acceptedJul 25. 1995. March 1996. Vol. 86. No. 3

Smoking among Chinese Children

Government statistics show that 99.7% of children 7 years of age entered elementary schools in Beijing during 1988, and the annual dropout rate was about 3%.11 In total, 741 982 elementary school students, of whom 318 648 were in grades 4 to 6, attended 3875 schools. We used a two-stage stratified cluster sampling method. At the first stage, we stratified the 3875 elementary schools into urban schools (i.e., those in the city proper and the county towns) or rural schools (i.e., those in the outlying areas of the counties), and we randomly chose schools from each stratum. At the second stage, we randomly selected classes from schools. We calculated the number of classes to be chosen from each school such that the number of students for each stratum was proportional to the stratum size. The mean class size in the sample was 35.5, with a standard deviation of 9.8. Once a class was selected, we surveyed all students in the class. The sampling process was similar to that used in a previous report on junior high school students.12 In total, 479 classes from 122 elementary schools were chosen, and the total number of students surveyed was 17 035. In a 1987 survey conducted in four elementary school classes, 2.5% of the students reported that they currently smoked (Beijing Education Bureau, unpublished data, 1987). Based on previous studies in China,7'8 we anticipated the nonparticipation rate to be less than 10%. Using the formula provided by Snedecor and William,13 we calculated the required sample size to be approximately 17 000 in order for the "true" smoking prevalence not to differ by more than 10% from the estimated prevalence (at a 95% confidence level). Among the 17 035 students selected, 26 were absent during the survey; another 13 were excluded because their survey forms were unusable. The effective sample size was 16996 (8843 boys and 8153 girls), yielding a response rate of 99.8%.

Survey Methods Trained interviewers approached the teachers of the selected classes and the school principals 1 to 2 weeks before the survey to request cooperation and collaboration with survey procedures. All selected schools agreed to participate. On the date of the survey, students in a selected class were asked by their teacher to meet in their classroom. After a brief introduction, the teacher left the classroom and the interviewer explained the purpose and process of the survey to the March 1996, Vol. 86, No. 3

TABLE 1-Cigarette Smoking Patterns among Elementary School Students Who Reported Smoking during the Past 30 Days: Beijing, 1988

Boys

Question and Response

Girls %

No.

%

1214 221 17 21 16 9

81.0 14.8 1.2 1.4 1.1 0.6

98 9 0 2 9 0

83.1 7.6 0.0 2.0 7.4 0.0

114 1443 328

6.0 76.6 17.4

14 119 14

9.4 81.0 9.6

627 404 773

34.8 22.4 42.8

50 44 32

39.8 34.8 25.4

386 119 967 297

21.8 6.7 54.7 16.8

51 5 39 32

40.0 3.7 31.0 25.3

No.

On average, how many cigarettes do you smoke per day? 20 When you smoke, do you usually inhale or not? Inhale Just take the smoke into my mouth Both, can't say which is more often What kind of cigarettes do you usually

smoke? Filtered Nonfiltered Both, can't say which is more often Where do you usually get your cigarettes? Home Buy them myself Schoolmates/friends Other

students. To reduce the possibility of underreporting by smokers, the interviewer emphasized strongly that the survey was anonymous and that individual responses would not be disclosed to teachers or parents. The interviewer stayed in the classroom during the entire process to maintain order and answer the students' questions. We did not use biological markers to validate smoking status reported by respondents because this would have enormously increased our costs, given the large sample size, and because most practical biological markers are either insensitive or nonspecific in detecting very infrequent and light smoking. Also, tests based on biological markers among children can be easily biased by parental smoking. However, we attempted to minimize possible underreporting by smokers by using a self-administered anonymous questionnaire, strongly emphasizing the anonymity of questionnaire responses, and asking the teachers to leave the classroom during the survey. We collected the following information: (1) social and demographic data; (2) smoking status; (3) familial and psychosocial risk factors for smoking; (4) age at, setting of, and reason for smoking initiation; and (5) smoking patterns, including daily cigarette consumption, inhalation

practices, type of cigarettes (filtered or nonfiltered) smoked, and usual source of cigarettes. (We asked only students who had smoked during the previous 30 days to complete the smoking patterns portion of the questionnaire because, in a pilot study, many students who had not smoked during the previous 30 days skipped this section.) We classified students into four categories based on their self-reported smoking status. Daily smokers smoked every day (those who stopped daily smoking only on special occasions, such as when they were sick, were included in this category); weekly smokers smoked at least once a week but not daily; occasional smokers smoked less than once a week or only on some special occasions or had smoked just a few times; and never smokers had never tried a cigarette. In the polychotomous logistic regression analysis, we further collapsed daily and weekly smokers into one category because the small numbers in the separate subcategories would have resulted in unstable odds ratio estimates. We refer to these students as regular smokers. In addition, we defined students as current smokers if they had smoked during the previous 30 days, as inhaling smokers if they often inhaled, and as mouth smokers if they took smoke into their mouth and puffed out immediAmerican Journal of Public Health 369

Zhu et al.

TABLE 2-First Cigarette Smoking Experience of Elementary School Students Who Reported Ever Smoking Cigarettes: Beijing, 1988

Girls

Boys

Question and Response

No.

%

No.

%

144 924 1008

6.9 44.5 48.6

20 88 62

11.6 51.9 36.5

78 9 138 11 197 547 301 5 140

5.5 0.6 9.7 0.8 13.8 38.4 21.1 0.4 9.8

9 1 14 4 13 48 8 1 11

8.3 0.9 12.8 3.7 11.9 44.0 7.3 0.9 10.1

469 137 124 204 563

31.3 9.2 8.3 13.6 37.6

84 4 3 24 28

58.7 2.8 2.1 16.8 19.6

90

4.1

4

2.6

760 624 221 470

35.1 28.8 10.2 21.7

66 38 13 47

39.2 22.4 8.0 27.8

341 993 196 100 95

19.8 57.6 11.4 5.8 5.5

28 66 12 30 5

19.9 46.8 8.5 21.3 3.5

At what age did you first try a cigarette?