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The majority of adult tobacco smokers take up smoking during adolescence. A number of stages in the pathway to becoming a regular smoker during adolescence have been described including triers, experimenters, regular users and dependent users.1Cohort studies of adolescents have identified various trajectories through these stages to adult smoking, which combine measures of stability in smoking status over time along with early/rapid or late/slow adopters of smoking.2-6 However, once adolescents start trying or experimenting with smoking, the transition is mostly a one way process towards regular smoking,7 although some smokers start quitting in their early 20s.2 5 An early review of the predictors of youth smoking concluded that there was a high level of support for social learning variables, such as peer and family smoking, being involved in the initiation of tobacco smoking.8 In particular, the review found stronger evidence for an effect from peer smoking than for parental smoking. However, subsequent reports have provided conflicting evidence with regard to this conclusion. A Californian cohort study observed that friends smoking had a stronger effect on adolescent smoking behaviour, particularly initiation, than parental smoking;9 although a subsequent report from this study found that, while smoking by friends was important in the transition from trial to experimental smoking, parental smoking predicted the transition from experimental to regular smoking.10 The latter finding is supported by a US Mid-West cohort study which found that parental smoking was associated with regular smoking in adolescence and adulthood, but not with adolescent smoking experimentation; although the parental effects were not as strong as peer effects.2 In contrast, a New Zealand cohort study observed that parental smoking predicted smoking experimentation by age 13 years, while smoking at age 16 years was most strongly predicted by affiliation with smoking peers at 15 years.11 Further, the US National Longitudinal Study of Adolescent Health concluded that adolescent smoking is more influenced by friend smoking than parent smoking, after comparing the relative sizes of the risk ratios for these two variables.12 A recent review has concluded, based on the strengths of relative risks, that peer or friend smoking is more strongly related to adolescent smoking than parental smoking.13 However, this conclusion has recently been challenged by the argument that the preferred measure of effect for ranking public health risk factors is the population attributable risk, which integrates into a single measure both the strength of a risk factor (i.e. the relative risk) and its frequency (prevalence).14 The population attributable risk (or fraction) can be interpreted as the proportion of outcome events (e.g. adolescent smoking) that can be attributed to (or explained by) an exposure variable (assuming the latter is causative).15 Applying this calculation to a national sample of New Zealand Year 10 students produced attributable risk values of 67% for best friend smoking and 64% for parental smoking combined with exposures under parental control such as allowing smoking in the home or amount of pocket money.14 Further, the influence of parents precedes that of peers, and previous studies which have controlled for the effect of friend and older sibling smoking in multivariate analyses will have underestimated the effect of parental smoking.16 17 In this current paper we extend earlier results from the national Year 10 (aged 14 -15 years) surveys by comparing the relative importance of the influence of parental smoking and best friend smoking on the various stages of adolescent smoking, along the continuum from being a never smoker susceptible to smoking, to becoming a daily smoker. Method Annual national surveys of tobacco smoking by Year 10 (4th form) students (ages 14-15 years) have been carried out yearly since 1999.18 Each year, all New Zealand schools with Year 10 students were invited to participate in the survey by administering a short questionnaire to their Year 10 students in November. The current paper reports data from the 2002-2006 surveys which collected information on smoking by parents and best friend of students. The annual school response rate was 67% in 2002 (n = 309), 66% in 2003 (n = 312), 65% in 2004 (n = 319), 58% (n = 278) in 2005, and 78% (n = 291) in 2006. The Ethics Committee of the Ministry of Health in Auckland granted a waiver of the formal review and consenting processes. School principals gave permission for teachers to supervise students while they completed the anonymous self-administered questionnaires in class. To maintain confidentiality, teachers did not examine the surveys for completeness. Students answered a two-page questionnaire, which included questions on age, sex and ethnicity (self-assigned). Because students could choose more than one ethnic group, a priority system was used to classify any student choosing M ori as such, then any Pacific student as such, followed by any Asian student as such, followed by European. Students answered whether their mother, father or best friend smoked; and whether people were allowed to smoke inside their house. With regard to their own smoking status, students were asked cHave you ever smoked a cigarette, even just a few puffs?d, and if they answered cyesd, they were asked chow often do you smoke now?d Those who answered cnod to both questions were classified as never smokers, while those who answered cyesd to the first question and cnod to the second were classified as experimenters. Those who answered cyesd were queried about the frequency of their current smoking (at least once a day, at least once a week, at least once a month, less often, never). Susceptibility to future smoking was assessed by asking cDo you think you will smoke a cigarette at any time during the next year?d Respondents were classified as non-susceptible only if they answered definitely not. Similar measures of susceptibility have been shown to predict experimentation with tobacco smoking in previous youth cohort studies.19,20 Students smoking monthly or more often were asked their age (in years) when they first started smoking monthly (for the years 2003-2005). The total number of completed questionnaires returned by schools during the 5 year period was 167,488 (30,972 in 2002, 34,812 in 2003, 33,279 in 2004, 34,038 in 2005, and 34,387 in 2006), out of 229,240 on school rolls (73.1% student response). Analyses were restricted to 162,931 students who were 14 and 15 years old. We further excluded students with missing data for gender (n=509), ethnicity (n=1283), student smoking status (n=1,291), and parent or best friend smoking status (n=2,211). This left 157,637 students available for analyses. All statistical analyses were made using SAS callable SUDAAN (Release 9.0.1, 2005) which corrects standard errors and confidence intervals for any design effect from clustering of students by school. The CROSSTAB procedure was use to calculate relative risks, and the MULTILOG procedure was used to calculate adjusted odds ratios (OR) while adjusting for age, gender and ethnicity, and to test for interaction. The population attributable risk was calculated by estimating the attributable proportion for the exposed cases within each exposure category using standard methods.21 Results The distribution of smoking status, by level of demographic variable and smoking status of parents and best friend, is shown in Table 1. Age was associated with an increased risk of smoking, with a higher proportion 15-year-old students distributed in the smoking categories than 14-year-old students (p<0.0001). Girls were more likely to be smokers than boys, who had a higher proportion of never smokers (49.3% v. 43.3%, p<0.0001). With regard to ethnicity, smoking levels were highest among M ori students, followed in order by Pacific, European and Asian (p<0.0001). Students who lived in a house where smoking was allowed were three times more likely to be daily smokers than those who did not (20.7% v. 6.3%, p<0.0001). When students were categorised by the smoking status of their parents and best friend, student smoking levels were highest among those with both parents and best friend being smokers (41.1% daily smokers), followed by students who had non-smoking parents but their best friend smoked (19.1% daily smokers), and by students with smoking parents but best friend a non-smoker (5.4% daily smokers), while smoking was lowest among students with neither parents nor best friend being smokers (1.8% daily smokers). Students were more likely to be exposed to parental smoking (40%) than best friend smoking (25%). Table 2 shows the relative risk of never smoking students being susceptible to smoking in the next year, associated with parental and best friend smoking. Students of non-smoking parents with a best friend who smoked were most likely to think they would smoke during the next year (47.9%), followed by students with both parents and best friend being smokers (41.4%). Table 2. Relative risk, and attributable risk, of a never smoker being susceptible to smoking in next year. Parent smokes Best friend smokes Susceptible Relative Risk (95%CI)# Attributable cases Population attributable risk+ Yes N (%)* No N Yes Yes 918 (41.4%) 1297 1.45 (1.3731.53) 285 1.3% Yes No 5449 (31.2%) 12,041 1.10 (1.0631.13) 495 2.2% No Yes 1615 (47.9%) 1755 1.63 (1.5731.70) 624 2.8% No No 14,413 (29.0%) 35,219 1.00 3 3 Total 22,395 50,312 1404 6.3% *Percent of total of each parent-friend smoking category; # Adjusted for age, sex and ethnicity; +Attributable cases / total number of susceptible. The effect of parental smoking by itself was weak, with only a 10% relative increase in the risk of being susceptible (to 31.2%) compared with the reference category of students with neither parents nor best friend being smokers (29.0% susceptible). The population attributable risk, which gives the proportion of susceptible students that can be explained by parental and/or best friend smoking, was only 6.3%, indicating that susceptibility is explained primarily by other risk factors. A stronger effect from parental and best friend smoking was seen on the risk of current non-smokers having ever experimented with cigarettes (Table 3). The relative risk (RR) of being an experimenter was highest for students with both parents and best friend being a smoker (RR = 2.01) or with best friend only being a smoker (RR = 1.83). However, the attributable risk value was highest for students with parents only being smokers (11.9%) because students in this category made up a greater proportion (29%) of all students not currently smoking compared to the previous two categories (each 6%). Collectively, 21.7% of current non-smoking students who had ever experimented with cigarettes could be explained by parental and/or best friend smoking. The relative and attributable risks of current student smoking associated with parent and best friend smoking are shown in Table 4. The general pattern for less than daily smoking by students was for the effect to be strongest for best friend smoking alone, followed by both parent and best friend smoking, with parent smoking alone having the lowest relative risks within each of these student smoking categories. In contrast, for daily smoking, the effect of both parent and best friend smoking combined (RR = 14.29) was more than the sum of the net effect of parent smoking alone (RR = 2.19) and best friend alone (RR = 8.25). This interaction was statistically significant (p<0.0001). More than half of student daily smokers (53.9%) could be attributed to the combined effect of parent and best friend smoking. The other important feature of the results in this table is the progressive increase in the population attributable risk values with increasing frequency of smoking: from 28.3% for students smoking less than monthly up to 78.7% for those smoking daily. The pattern in Table 4 occurred within each sex, with parental and best friend smoking, separately and together, being significantly (p<0.01) associated with all frequencies of adolescent smoking (data not shown). Table 3. Relative risk, and attributable risk, of a non-smoker having ever experimented with cigarettes Parent smokes Best friend smokes Experimented Relative Risk (95%CI)# Attributable cases Population attributable risk+ Yes N (%)* No N Yes Yes 4553 (66.9%) 2250 2.01 (1.9432.07) 2288 5.4% Yes No 14,742 (45.6%) 17,610 1.52 (1.4931.55) 5043 11.9% No Yes 4098 (54.7%) 3401 1.83 (1.7831.89) 1859 4.4% No No 19,028 (27.6%) 49,858 1.00 - - Total 42,421 73,119 9190 21.7% *Percent of total of each parent-friend smoking category; #Adjusted for age, sex and ethnicity; +Attributable cases / total number of experimenters. Table 4. Relative risk and attributable risk of smoking, associated with smoking by parent and best friend, by frequency of student smoking. Parent smokes Best friend smokes N (%)* in smoking category Relative Risk (95% CI)# Attributable cases Population attributable risk+ Smoking < Monthly Yes Yes 2672 (11.7%) 1.82 (1.7231.93) 1204 9.0% Yes No 3519 (8.7%) 1.41 (1.3431.48) 1023 7.6% No Yes 2665 (15.8%) 2.44 (2.3232.58) 1573 11.7% No No 4589 (5.9%) 1.00 - - Total 13,445 3800 28.3% Monthly smoking Yes Yes 1648 (7.2%) 3.15 (2.9033.42) 1125 18.0% Yes No 1344 (3.3%) 1.54 (1.4331.67) 471 7.5% No Yes 1707 (10.1%) 4.43 (4.1034.79) 1322 21.2% No No 1549 (2.0%) 1.00 - - Total 6248 2918 46.7% Weekly smoking Yes Yes 2321 (10.2%) 5.83 (5.2836.44) 1923 30.7% Yes No 1084 (2.7%) 1.72 (1.5731.89) 454 7.2% No Yes 1821 (10.8%) 6.69 (6.1337.30) 1549 24.7% No No 1035 (1.3%) 1.00 - - Total 6261 3926 62.7% Daily smoking Yes Yes 9361 (41.1%) 14.29 (13.1315.6) 8706 53.9% Yes No 2170 (5.4%) 2.19 (2.0332.36) 1179 7.3% No Yes 3214 (19.0%) 8.25 (7.5738.99) 2824 17.5% No No 1398 (1.8%) 1.00 - - Total 16,143 12,709 78.7% * Percent of total of each parent-friend smoking category; #Adjusted for age, sex and ethnicity; +Attributable cases / total number of smokers in same smoking frequency category. Controlling for smoking in the house greatly reduced the relative risks associated with parental smoking, with this confounding effect weakening with reducing frequency of student smoking. For example, compared to students not exposed to parent nor to best friend smoking, the RR of daily smoking in students exposed to both parent and best friend smoking decreased from 14.49 shown in Table 4 to 9.51 (95%CI: 8.74310.36) with additional adjustment for smoking in the house; while the RR of smoking less than monthly for the same exposure declined from 1.82 in Table 4 to 1.67 (95%CI: 1.5731.79) with additional adjustment for smoking in the house. There was an inverse association between age of starting smoking and frequency of smoking (Table 5). Students who smoked daily were nearly twice as likely to have started smoking by the age of 9 years (18.2%) than students smoking weekly (11.8%) or monthly (10.1%). Table 5. Distribution of age students started smoking monthly, up to 13 years, by current frequency of smoking: 200332005 Age started smoking monthly (years) Smoking frequency

Summary

Abstract

Aim

Compare the effect of parental and best friend smoking across the stages of adolescent smoking, from being a never smoker susceptible to smoking, to being a daily smoker

Method

National cross-sectional annual survey (2002-2006 combined) of 157,637 Year 10 students aged 14 and 15 years who answered an anonymous self-administered questionnaire.

Results

The effects of smoking by parents and best friend varied with stage of adolescent tobacco smoking. Attributable risk calculations showed that parental and best friend smoking explained only 6.3% of susceptibility to smoking among never smokers, and 21.7% of non-smoking students who had ever experimented with cigarettes. The attributable risk for parental and best friend smoking progressively increased with smoking frequency, up to 78.7% for daily smoking. The effect of best friend smoking was stronger than parental smoking, although there was a synergistic effect of both variables on the risk of daily smoking.

Conclusion

Smoking by best friend and parents are strongly associated with current smoking by adolescents, but unrelated to susceptibility to smoke among those who are non-smokers.

Author Information

Acknowledgements

The surveys were carried out by Action on Smoking and Health (ASH), with assistance of the Health Sponsorship Council of New Zealand in 2006. The New Zealand Ministry of Health provided funds.

Correspondence

Assoc Prof Robert Scragg, Epidemiology & Biostatistics, School of Population Health, University of Auckland, Private Bag, Auckland, New Zealand. Fax: +64 (0)9 3737503

Correspondence Email

r.scragg@auckland.ac.nz

Competing Interests

- Mayhew KP, Flay BR, Mott JA. Stages in the development of adolescent smoking. Drug Alcohol Depend 2000;59 Suppl 1:S61-81.-- Chassin L, Presson CC, Pitts SC, Sherman SJ. The natural history of cigarette smoking from adolescence to adulthood in a midwestern community sample: multiple trajectories and their psychosocial correlates. Health Psychol 2000;19(3):223-31.-- Colder CR, Mehta P, Balanda K, et al. Identifying trajectories of adolescent smoking: an application of latent growth mixture modeling. Health Psychol 2001;20(2):127-35.-- Soldz S, Cui X. Pathways through adolescent smoking: a 7-year longitudinal grouping analysis. Health Psychol 2002;21(5):495-504.-- White HR, Pandina RJ, Chen PH. Developmental trajectories of cigarette use from early adolescence into young adulthood. Drug Alcohol Depend 2002;65(2):167-78.-- Audrain-McGovern J, Rodriguez D, Tercyak KP, et al. Identifying and characterizing adolescent smoking trajectories. Cancer Epidemiol Biomarkers Prev 2004;13(12):2023-34.-- Fergusson DM, Horwood LJ. Transitions to cigarette smoking during adolescence. Addict Behav 1995;20(5):627-42.-- Conrad KM, Flay BR, Hill D. Why children start smoking cigarettes: predictors of onset. Br J Addict 1992;87(12):1711-24.-- Flay BR, Hu FB, Siddiqui O, et al. Differential influence of parental smoking and friends' smoking on adolescent initiation and escalation of smoking. J Health Soc Behav 1994;35(3):248-65.-- Flay BR, Hu FB, Richardson J. Psychosocial predictors of different stages of cigarette smoking among high school students. Prev Med 1998;27(5 Pt 3):A9-18.-- Fergusson DM, Lynskey MT, Horwood LJ. The role of peer affiliations, social, family and individual factors in continuities in cigarette smoking between childhood and adolescence. Addiction 1995;90(5):647-59.-- Bauman KE, Carver K, Gleiter K. Trends in parent and friend influence during adolescence: the case of adolescent cigarette smoking. Addict Behav 2001;26(3):349-61.-- Avenevoli S, Merikangas KR. Familial influences on adolescent smoking. Addiction 2003;98 Suppl 1:1-20.-- Scragg R, Laugesen M. Influence of smoking by family and best friend on adolescent tobacco smoking: results from the 2002 New Zealand national survey of year 10 students. Aust N Z J Public Health 2007;31(3):217-23.-- Last JM. A Dictionary of Epidemiology. 4th ed. New York: OUP, 2001.-- Darling N, Cumsille P. Theory, measurement, and methods in the study of family influences on adolescent smoking. Addiction 2003;98 Suppl 1:21-36.-- Kobus K. Peers and adolescent smoking. Addiction 2003;98 Suppl 1:37-55.-- Scragg R. Report of 1999-2006 National Year 10 Smoking Surveys. Auckland: Action on Smoking and Health (ASH), 2007:1-58.-- Pierce JP, Choi WS, Gilpin EA, et al. Validation of susceptibility as a predictor of which adolescents take up smoking in the United States. Health Psychol 1996;15(5):355-61.-- Unger JB, Johnson CA, Stoddard JL, et al. Identification of adolescents at risk for smoking initiation: validation of a measure of susceptibility. Addict Behav 1997;22(1):81-91.-- Rockhill B, Newman B, Weinberg C. Use and misuse of population attributable fractions. Am J Public Health 1998;88(1):15-9.-- Robinson ML, Berlin I, Moolchan ET. Tobacco smoking trajectory and associated ethnic differences among adolescent smokers seeking cessation treatment. J Adolesc Health 2004;35(3):217-24.-- Thomas R, Perera R. School-based programmes for preventing smoking. Cochrane Database of Systematic Reviews, 2006:Issue 3. 1-166. No.: CD001293.-

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The majority of adult tobacco smokers take up smoking during adolescence. A number of stages in the pathway to becoming a regular smoker during adolescence have been described including triers, experimenters, regular users and dependent users.1Cohort studies of adolescents have identified various trajectories through these stages to adult smoking, which combine measures of stability in smoking status over time along with early/rapid or late/slow adopters of smoking.2-6 However, once adolescents start trying or experimenting with smoking, the transition is mostly a one way process towards regular smoking,7 although some smokers start quitting in their early 20s.2 5 An early review of the predictors of youth smoking concluded that there was a high level of support for social learning variables, such as peer and family smoking, being involved in the initiation of tobacco smoking.8 In particular, the review found stronger evidence for an effect from peer smoking than for parental smoking. However, subsequent reports have provided conflicting evidence with regard to this conclusion. A Californian cohort study observed that friends smoking had a stronger effect on adolescent smoking behaviour, particularly initiation, than parental smoking;9 although a subsequent report from this study found that, while smoking by friends was important in the transition from trial to experimental smoking, parental smoking predicted the transition from experimental to regular smoking.10 The latter finding is supported by a US Mid-West cohort study which found that parental smoking was associated with regular smoking in adolescence and adulthood, but not with adolescent smoking experimentation; although the parental effects were not as strong as peer effects.2 In contrast, a New Zealand cohort study observed that parental smoking predicted smoking experimentation by age 13 years, while smoking at age 16 years was most strongly predicted by affiliation with smoking peers at 15 years.11 Further, the US National Longitudinal Study of Adolescent Health concluded that adolescent smoking is more influenced by friend smoking than parent smoking, after comparing the relative sizes of the risk ratios for these two variables.12 A recent review has concluded, based on the strengths of relative risks, that peer or friend smoking is more strongly related to adolescent smoking than parental smoking.13 However, this conclusion has recently been challenged by the argument that the preferred measure of effect for ranking public health risk factors is the population attributable risk, which integrates into a single measure both the strength of a risk factor (i.e. the relative risk) and its frequency (prevalence).14 The population attributable risk (or fraction) can be interpreted as the proportion of outcome events (e.g. adolescent smoking) that can be attributed to (or explained by) an exposure variable (assuming the latter is causative).15 Applying this calculation to a national sample of New Zealand Year 10 students produced attributable risk values of 67% for best friend smoking and 64% for parental smoking combined with exposures under parental control such as allowing smoking in the home or amount of pocket money.14 Further, the influence of parents precedes that of peers, and previous studies which have controlled for the effect of friend and older sibling smoking in multivariate analyses will have underestimated the effect of parental smoking.16 17 In this current paper we extend earlier results from the national Year 10 (aged 14 -15 years) surveys by comparing the relative importance of the influence of parental smoking and best friend smoking on the various stages of adolescent smoking, along the continuum from being a never smoker susceptible to smoking, to becoming a daily smoker. Method Annual national surveys of tobacco smoking by Year 10 (4th form) students (ages 14-15 years) have been carried out yearly since 1999.18 Each year, all New Zealand schools with Year 10 students were invited to participate in the survey by administering a short questionnaire to their Year 10 students in November. The current paper reports data from the 2002-2006 surveys which collected information on smoking by parents and best friend of students. The annual school response rate was 67% in 2002 (n = 309), 66% in 2003 (n = 312), 65% in 2004 (n = 319), 58% (n = 278) in 2005, and 78% (n = 291) in 2006. The Ethics Committee of the Ministry of Health in Auckland granted a waiver of the formal review and consenting processes. School principals gave permission for teachers to supervise students while they completed the anonymous self-administered questionnaires in class. To maintain confidentiality, teachers did not examine the surveys for completeness. Students answered a two-page questionnaire, which included questions on age, sex and ethnicity (self-assigned). Because students could choose more than one ethnic group, a priority system was used to classify any student choosing M ori as such, then any Pacific student as such, followed by any Asian student as such, followed by European. Students answered whether their mother, father or best friend smoked; and whether people were allowed to smoke inside their house. With regard to their own smoking status, students were asked cHave you ever smoked a cigarette, even just a few puffs?d, and if they answered cyesd, they were asked chow often do you smoke now?d Those who answered cnod to both questions were classified as never smokers, while those who answered cyesd to the first question and cnod to the second were classified as experimenters. Those who answered cyesd were queried about the frequency of their current smoking (at least once a day, at least once a week, at least once a month, less often, never). Susceptibility to future smoking was assessed by asking cDo you think you will smoke a cigarette at any time during the next year?d Respondents were classified as non-susceptible only if they answered definitely not. Similar measures of susceptibility have been shown to predict experimentation with tobacco smoking in previous youth cohort studies.19,20 Students smoking monthly or more often were asked their age (in years) when they first started smoking monthly (for the years 2003-2005). The total number of completed questionnaires returned by schools during the 5 year period was 167,488 (30,972 in 2002, 34,812 in 2003, 33,279 in 2004, 34,038 in 2005, and 34,387 in 2006), out of 229,240 on school rolls (73.1% student response). Analyses were restricted to 162,931 students who were 14 and 15 years old. We further excluded students with missing data for gender (n=509), ethnicity (n=1283), student smoking status (n=1,291), and parent or best friend smoking status (n=2,211). This left 157,637 students available for analyses. All statistical analyses were made using SAS callable SUDAAN (Release 9.0.1, 2005) which corrects standard errors and confidence intervals for any design effect from clustering of students by school. The CROSSTAB procedure was use to calculate relative risks, and the MULTILOG procedure was used to calculate adjusted odds ratios (OR) while adjusting for age, gender and ethnicity, and to test for interaction. The population attributable risk was calculated by estimating the attributable proportion for the exposed cases within each exposure category using standard methods.21 Results The distribution of smoking status, by level of demographic variable and smoking status of parents and best friend, is shown in Table 1. Age was associated with an increased risk of smoking, with a higher proportion 15-year-old students distributed in the smoking categories than 14-year-old students (p<0.0001). Girls were more likely to be smokers than boys, who had a higher proportion of never smokers (49.3% v. 43.3%, p<0.0001). With regard to ethnicity, smoking levels were highest among M ori students, followed in order by Pacific, European and Asian (p<0.0001). Students who lived in a house where smoking was allowed were three times more likely to be daily smokers than those who did not (20.7% v. 6.3%, p<0.0001). When students were categorised by the smoking status of their parents and best friend, student smoking levels were highest among those with both parents and best friend being smokers (41.1% daily smokers), followed by students who had non-smoking parents but their best friend smoked (19.1% daily smokers), and by students with smoking parents but best friend a non-smoker (5.4% daily smokers), while smoking was lowest among students with neither parents nor best friend being smokers (1.8% daily smokers). Students were more likely to be exposed to parental smoking (40%) than best friend smoking (25%). Table 2 shows the relative risk of never smoking students being susceptible to smoking in the next year, associated with parental and best friend smoking. Students of non-smoking parents with a best friend who smoked were most likely to think they would smoke during the next year (47.9%), followed by students with both parents and best friend being smokers (41.4%). Table 2. Relative risk, and attributable risk, of a never smoker being susceptible to smoking in next year. Parent smokes Best friend smokes Susceptible Relative Risk (95%CI)# Attributable cases Population attributable risk+ Yes N (%)* No N Yes Yes 918 (41.4%) 1297 1.45 (1.3731.53) 285 1.3% Yes No 5449 (31.2%) 12,041 1.10 (1.0631.13) 495 2.2% No Yes 1615 (47.9%) 1755 1.63 (1.5731.70) 624 2.8% No No 14,413 (29.0%) 35,219 1.00 3 3 Total 22,395 50,312 1404 6.3% *Percent of total of each parent-friend smoking category; # Adjusted for age, sex and ethnicity; +Attributable cases / total number of susceptible. The effect of parental smoking by itself was weak, with only a 10% relative increase in the risk of being susceptible (to 31.2%) compared with the reference category of students with neither parents nor best friend being smokers (29.0% susceptible). The population attributable risk, which gives the proportion of susceptible students that can be explained by parental and/or best friend smoking, was only 6.3%, indicating that susceptibility is explained primarily by other risk factors. A stronger effect from parental and best friend smoking was seen on the risk of current non-smokers having ever experimented with cigarettes (Table 3). The relative risk (RR) of being an experimenter was highest for students with both parents and best friend being a smoker (RR = 2.01) or with best friend only being a smoker (RR = 1.83). However, the attributable risk value was highest for students with parents only being smokers (11.9%) because students in this category made up a greater proportion (29%) of all students not currently smoking compared to the previous two categories (each 6%). Collectively, 21.7% of current non-smoking students who had ever experimented with cigarettes could be explained by parental and/or best friend smoking. The relative and attributable risks of current student smoking associated with parent and best friend smoking are shown in Table 4. The general pattern for less than daily smoking by students was for the effect to be strongest for best friend smoking alone, followed by both parent and best friend smoking, with parent smoking alone having the lowest relative risks within each of these student smoking categories. In contrast, for daily smoking, the effect of both parent and best friend smoking combined (RR = 14.29) was more than the sum of the net effect of parent smoking alone (RR = 2.19) and best friend alone (RR = 8.25). This interaction was statistically significant (p<0.0001). More than half of student daily smokers (53.9%) could be attributed to the combined effect of parent and best friend smoking. The other important feature of the results in this table is the progressive increase in the population attributable risk values with increasing frequency of smoking: from 28.3% for students smoking less than monthly up to 78.7% for those smoking daily. The pattern in Table 4 occurred within each sex, with parental and best friend smoking, separately and together, being significantly (p<0.01) associated with all frequencies of adolescent smoking (data not shown). Table 3. Relative risk, and attributable risk, of a non-smoker having ever experimented with cigarettes Parent smokes Best friend smokes Experimented Relative Risk (95%CI)# Attributable cases Population attributable risk+ Yes N (%)* No N Yes Yes 4553 (66.9%) 2250 2.01 (1.9432.07) 2288 5.4% Yes No 14,742 (45.6%) 17,610 1.52 (1.4931.55) 5043 11.9% No Yes 4098 (54.7%) 3401 1.83 (1.7831.89) 1859 4.4% No No 19,028 (27.6%) 49,858 1.00 - - Total 42,421 73,119 9190 21.7% *Percent of total of each parent-friend smoking category; #Adjusted for age, sex and ethnicity; +Attributable cases / total number of experimenters. Table 4. Relative risk and attributable risk of smoking, associated with smoking by parent and best friend, by frequency of student smoking. Parent smokes Best friend smokes N (%)* in smoking category Relative Risk (95% CI)# Attributable cases Population attributable risk+ Smoking < Monthly Yes Yes 2672 (11.7%) 1.82 (1.7231.93) 1204 9.0% Yes No 3519 (8.7%) 1.41 (1.3431.48) 1023 7.6% No Yes 2665 (15.8%) 2.44 (2.3232.58) 1573 11.7% No No 4589 (5.9%) 1.00 - - Total 13,445 3800 28.3% Monthly smoking Yes Yes 1648 (7.2%) 3.15 (2.9033.42) 1125 18.0% Yes No 1344 (3.3%) 1.54 (1.4331.67) 471 7.5% No Yes 1707 (10.1%) 4.43 (4.1034.79) 1322 21.2% No No 1549 (2.0%) 1.00 - - Total 6248 2918 46.7% Weekly smoking Yes Yes 2321 (10.2%) 5.83 (5.2836.44) 1923 30.7% Yes No 1084 (2.7%) 1.72 (1.5731.89) 454 7.2% No Yes 1821 (10.8%) 6.69 (6.1337.30) 1549 24.7% No No 1035 (1.3%) 1.00 - - Total 6261 3926 62.7% Daily smoking Yes Yes 9361 (41.1%) 14.29 (13.1315.6) 8706 53.9% Yes No 2170 (5.4%) 2.19 (2.0332.36) 1179 7.3% No Yes 3214 (19.0%) 8.25 (7.5738.99) 2824 17.5% No No 1398 (1.8%) 1.00 - - Total 16,143 12,709 78.7% * Percent of total of each parent-friend smoking category; #Adjusted for age, sex and ethnicity; +Attributable cases / total number of smokers in same smoking frequency category. Controlling for smoking in the house greatly reduced the relative risks associated with parental smoking, with this confounding effect weakening with reducing frequency of student smoking. For example, compared to students not exposed to parent nor to best friend smoking, the RR of daily smoking in students exposed to both parent and best friend smoking decreased from 14.49 shown in Table 4 to 9.51 (95%CI: 8.74310.36) with additional adjustment for smoking in the house; while the RR of smoking less than monthly for the same exposure declined from 1.82 in Table 4 to 1.67 (95%CI: 1.5731.79) with additional adjustment for smoking in the house. There was an inverse association between age of starting smoking and frequency of smoking (Table 5). Students who smoked daily were nearly twice as likely to have started smoking by the age of 9 years (18.2%) than students smoking weekly (11.8%) or monthly (10.1%). Table 5. Distribution of age students started smoking monthly, up to 13 years, by current frequency of smoking: 200332005 Age started smoking monthly (years) Smoking frequency

Summary

Abstract

Aim

Compare the effect of parental and best friend smoking across the stages of adolescent smoking, from being a never smoker susceptible to smoking, to being a daily smoker

Method

National cross-sectional annual survey (2002-2006 combined) of 157,637 Year 10 students aged 14 and 15 years who answered an anonymous self-administered questionnaire.

Results

The effects of smoking by parents and best friend varied with stage of adolescent tobacco smoking. Attributable risk calculations showed that parental and best friend smoking explained only 6.3% of susceptibility to smoking among never smokers, and 21.7% of non-smoking students who had ever experimented with cigarettes. The attributable risk for parental and best friend smoking progressively increased with smoking frequency, up to 78.7% for daily smoking. The effect of best friend smoking was stronger than parental smoking, although there was a synergistic effect of both variables on the risk of daily smoking.

Conclusion

Smoking by best friend and parents are strongly associated with current smoking by adolescents, but unrelated to susceptibility to smoke among those who are non-smokers.

Author Information

Acknowledgements

The surveys were carried out by Action on Smoking and Health (ASH), with assistance of the Health Sponsorship Council of New Zealand in 2006. The New Zealand Ministry of Health provided funds.

Correspondence

Assoc Prof Robert Scragg, Epidemiology & Biostatistics, School of Population Health, University of Auckland, Private Bag, Auckland, New Zealand. Fax: +64 (0)9 3737503

Correspondence Email

r.scragg@auckland.ac.nz

Competing Interests

- Mayhew KP, Flay BR, Mott JA. Stages in the development of adolescent smoking. Drug Alcohol Depend 2000;59 Suppl 1:S61-81.-- Chassin L, Presson CC, Pitts SC, Sherman SJ. The natural history of cigarette smoking from adolescence to adulthood in a midwestern community sample: multiple trajectories and their psychosocial correlates. Health Psychol 2000;19(3):223-31.-- Colder CR, Mehta P, Balanda K, et al. Identifying trajectories of adolescent smoking: an application of latent growth mixture modeling. Health Psychol 2001;20(2):127-35.-- Soldz S, Cui X. Pathways through adolescent smoking: a 7-year longitudinal grouping analysis. Health Psychol 2002;21(5):495-504.-- White HR, Pandina RJ, Chen PH. Developmental trajectories of cigarette use from early adolescence into young adulthood. Drug Alcohol Depend 2002;65(2):167-78.-- Audrain-McGovern J, Rodriguez D, Tercyak KP, et al. Identifying and characterizing adolescent smoking trajectories. Cancer Epidemiol Biomarkers Prev 2004;13(12):2023-34.-- Fergusson DM, Horwood LJ. Transitions to cigarette smoking during adolescence. Addict Behav 1995;20(5):627-42.-- Conrad KM, Flay BR, Hill D. Why children start smoking cigarettes: predictors of onset. Br J Addict 1992;87(12):1711-24.-- Flay BR, Hu FB, Siddiqui O, et al. Differential influence of parental smoking and friends' smoking on adolescent initiation and escalation of smoking. J Health Soc Behav 1994;35(3):248-65.-- Flay BR, Hu FB, Richardson J. Psychosocial predictors of different stages of cigarette smoking among high school students. Prev Med 1998;27(5 Pt 3):A9-18.-- Fergusson DM, Lynskey MT, Horwood LJ. The role of peer affiliations, social, family and individual factors in continuities in cigarette smoking between childhood and adolescence. Addiction 1995;90(5):647-59.-- Bauman KE, Carver K, Gleiter K. Trends in parent and friend influence during adolescence: the case of adolescent cigarette smoking. Addict Behav 2001;26(3):349-61.-- Avenevoli S, Merikangas KR. Familial influences on adolescent smoking. Addiction 2003;98 Suppl 1:1-20.-- Scragg R, Laugesen M. Influence of smoking by family and best friend on adolescent tobacco smoking: results from the 2002 New Zealand national survey of year 10 students. Aust N Z J Public Health 2007;31(3):217-23.-- Last JM. A Dictionary of Epidemiology. 4th ed. New York: OUP, 2001.-- Darling N, Cumsille P. Theory, measurement, and methods in the study of family influences on adolescent smoking. Addiction 2003;98 Suppl 1:21-36.-- Kobus K. Peers and adolescent smoking. Addiction 2003;98 Suppl 1:37-55.-- Scragg R. Report of 1999-2006 National Year 10 Smoking Surveys. Auckland: Action on Smoking and Health (ASH), 2007:1-58.-- Pierce JP, Choi WS, Gilpin EA, et al. Validation of susceptibility as a predictor of which adolescents take up smoking in the United States. Health Psychol 1996;15(5):355-61.-- Unger JB, Johnson CA, Stoddard JL, et al. Identification of adolescents at risk for smoking initiation: validation of a measure of susceptibility. Addict Behav 1997;22(1):81-91.-- Rockhill B, Newman B, Weinberg C. Use and misuse of population attributable fractions. Am J Public Health 1998;88(1):15-9.-- Robinson ML, Berlin I, Moolchan ET. Tobacco smoking trajectory and associated ethnic differences among adolescent smokers seeking cessation treatment. J Adolesc Health 2004;35(3):217-24.-- Thomas R, Perera R. School-based programmes for preventing smoking. Cochrane Database of Systematic Reviews, 2006:Issue 3. 1-166. No.: CD001293.-

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The majority of adult tobacco smokers take up smoking during adolescence. A number of stages in the pathway to becoming a regular smoker during adolescence have been described including triers, experimenters, regular users and dependent users.1Cohort studies of adolescents have identified various trajectories through these stages to adult smoking, which combine measures of stability in smoking status over time along with early/rapid or late/slow adopters of smoking.2-6 However, once adolescents start trying or experimenting with smoking, the transition is mostly a one way process towards regular smoking,7 although some smokers start quitting in their early 20s.2 5 An early review of the predictors of youth smoking concluded that there was a high level of support for social learning variables, such as peer and family smoking, being involved in the initiation of tobacco smoking.8 In particular, the review found stronger evidence for an effect from peer smoking than for parental smoking. However, subsequent reports have provided conflicting evidence with regard to this conclusion. A Californian cohort study observed that friends smoking had a stronger effect on adolescent smoking behaviour, particularly initiation, than parental smoking;9 although a subsequent report from this study found that, while smoking by friends was important in the transition from trial to experimental smoking, parental smoking predicted the transition from experimental to regular smoking.10 The latter finding is supported by a US Mid-West cohort study which found that parental smoking was associated with regular smoking in adolescence and adulthood, but not with adolescent smoking experimentation; although the parental effects were not as strong as peer effects.2 In contrast, a New Zealand cohort study observed that parental smoking predicted smoking experimentation by age 13 years, while smoking at age 16 years was most strongly predicted by affiliation with smoking peers at 15 years.11 Further, the US National Longitudinal Study of Adolescent Health concluded that adolescent smoking is more influenced by friend smoking than parent smoking, after comparing the relative sizes of the risk ratios for these two variables.12 A recent review has concluded, based on the strengths of relative risks, that peer or friend smoking is more strongly related to adolescent smoking than parental smoking.13 However, this conclusion has recently been challenged by the argument that the preferred measure of effect for ranking public health risk factors is the population attributable risk, which integrates into a single measure both the strength of a risk factor (i.e. the relative risk) and its frequency (prevalence).14 The population attributable risk (or fraction) can be interpreted as the proportion of outcome events (e.g. adolescent smoking) that can be attributed to (or explained by) an exposure variable (assuming the latter is causative).15 Applying this calculation to a national sample of New Zealand Year 10 students produced attributable risk values of 67% for best friend smoking and 64% for parental smoking combined with exposures under parental control such as allowing smoking in the home or amount of pocket money.14 Further, the influence of parents precedes that of peers, and previous studies which have controlled for the effect of friend and older sibling smoking in multivariate analyses will have underestimated the effect of parental smoking.16 17 In this current paper we extend earlier results from the national Year 10 (aged 14 -15 years) surveys by comparing the relative importance of the influence of parental smoking and best friend smoking on the various stages of adolescent smoking, along the continuum from being a never smoker susceptible to smoking, to becoming a daily smoker. Method Annual national surveys of tobacco smoking by Year 10 (4th form) students (ages 14-15 years) have been carried out yearly since 1999.18 Each year, all New Zealand schools with Year 10 students were invited to participate in the survey by administering a short questionnaire to their Year 10 students in November. The current paper reports data from the 2002-2006 surveys which collected information on smoking by parents and best friend of students. The annual school response rate was 67% in 2002 (n = 309), 66% in 2003 (n = 312), 65% in 2004 (n = 319), 58% (n = 278) in 2005, and 78% (n = 291) in 2006. The Ethics Committee of the Ministry of Health in Auckland granted a waiver of the formal review and consenting processes. School principals gave permission for teachers to supervise students while they completed the anonymous self-administered questionnaires in class. To maintain confidentiality, teachers did not examine the surveys for completeness. Students answered a two-page questionnaire, which included questions on age, sex and ethnicity (self-assigned). Because students could choose more than one ethnic group, a priority system was used to classify any student choosing M ori as such, then any Pacific student as such, followed by any Asian student as such, followed by European. Students answered whether their mother, father or best friend smoked; and whether people were allowed to smoke inside their house. With regard to their own smoking status, students were asked cHave you ever smoked a cigarette, even just a few puffs?d, and if they answered cyesd, they were asked chow often do you smoke now?d Those who answered cnod to both questions were classified as never smokers, while those who answered cyesd to the first question and cnod to the second were classified as experimenters. Those who answered cyesd were queried about the frequency of their current smoking (at least once a day, at least once a week, at least once a month, less often, never). Susceptibility to future smoking was assessed by asking cDo you think you will smoke a cigarette at any time during the next year?d Respondents were classified as non-susceptible only if they answered definitely not. Similar measures of susceptibility have been shown to predict experimentation with tobacco smoking in previous youth cohort studies.19,20 Students smoking monthly or more often were asked their age (in years) when they first started smoking monthly (for the years 2003-2005). The total number of completed questionnaires returned by schools during the 5 year period was 167,488 (30,972 in 2002, 34,812 in 2003, 33,279 in 2004, 34,038 in 2005, and 34,387 in 2006), out of 229,240 on school rolls (73.1% student response). Analyses were restricted to 162,931 students who were 14 and 15 years old. We further excluded students with missing data for gender (n=509), ethnicity (n=1283), student smoking status (n=1,291), and parent or best friend smoking status (n=2,211). This left 157,637 students available for analyses. All statistical analyses were made using SAS callable SUDAAN (Release 9.0.1, 2005) which corrects standard errors and confidence intervals for any design effect from clustering of students by school. The CROSSTAB procedure was use to calculate relative risks, and the MULTILOG procedure was used to calculate adjusted odds ratios (OR) while adjusting for age, gender and ethnicity, and to test for interaction. The population attributable risk was calculated by estimating the attributable proportion for the exposed cases within each exposure category using standard methods.21 Results The distribution of smoking status, by level of demographic variable and smoking status of parents and best friend, is shown in Table 1. Age was associated with an increased risk of smoking, with a higher proportion 15-year-old students distributed in the smoking categories than 14-year-old students (p<0.0001). Girls were more likely to be smokers than boys, who had a higher proportion of never smokers (49.3% v. 43.3%, p<0.0001). With regard to ethnicity, smoking levels were highest among M ori students, followed in order by Pacific, European and Asian (p<0.0001). Students who lived in a house where smoking was allowed were three times more likely to be daily smokers than those who did not (20.7% v. 6.3%, p<0.0001). When students were categorised by the smoking status of their parents and best friend, student smoking levels were highest among those with both parents and best friend being smokers (41.1% daily smokers), followed by students who had non-smoking parents but their best friend smoked (19.1% daily smokers), and by students with smoking parents but best friend a non-smoker (5.4% daily smokers), while smoking was lowest among students with neither parents nor best friend being smokers (1.8% daily smokers). Students were more likely to be exposed to parental smoking (40%) than best friend smoking (25%). Table 2 shows the relative risk of never smoking students being susceptible to smoking in the next year, associated with parental and best friend smoking. Students of non-smoking parents with a best friend who smoked were most likely to think they would smoke during the next year (47.9%), followed by students with both parents and best friend being smokers (41.4%). Table 2. Relative risk, and attributable risk, of a never smoker being susceptible to smoking in next year. Parent smokes Best friend smokes Susceptible Relative Risk (95%CI)# Attributable cases Population attributable risk+ Yes N (%)* No N Yes Yes 918 (41.4%) 1297 1.45 (1.3731.53) 285 1.3% Yes No 5449 (31.2%) 12,041 1.10 (1.0631.13) 495 2.2% No Yes 1615 (47.9%) 1755 1.63 (1.5731.70) 624 2.8% No No 14,413 (29.0%) 35,219 1.00 3 3 Total 22,395 50,312 1404 6.3% *Percent of total of each parent-friend smoking category; # Adjusted for age, sex and ethnicity; +Attributable cases / total number of susceptible. The effect of parental smoking by itself was weak, with only a 10% relative increase in the risk of being susceptible (to 31.2%) compared with the reference category of students with neither parents nor best friend being smokers (29.0% susceptible). The population attributable risk, which gives the proportion of susceptible students that can be explained by parental and/or best friend smoking, was only 6.3%, indicating that susceptibility is explained primarily by other risk factors. A stronger effect from parental and best friend smoking was seen on the risk of current non-smokers having ever experimented with cigarettes (Table 3). The relative risk (RR) of being an experimenter was highest for students with both parents and best friend being a smoker (RR = 2.01) or with best friend only being a smoker (RR = 1.83). However, the attributable risk value was highest for students with parents only being smokers (11.9%) because students in this category made up a greater proportion (29%) of all students not currently smoking compared to the previous two categories (each 6%). Collectively, 21.7% of current non-smoking students who had ever experimented with cigarettes could be explained by parental and/or best friend smoking. The relative and attributable risks of current student smoking associated with parent and best friend smoking are shown in Table 4. The general pattern for less than daily smoking by students was for the effect to be strongest for best friend smoking alone, followed by both parent and best friend smoking, with parent smoking alone having the lowest relative risks within each of these student smoking categories. In contrast, for daily smoking, the effect of both parent and best friend smoking combined (RR = 14.29) was more than the sum of the net effect of parent smoking alone (RR = 2.19) and best friend alone (RR = 8.25). This interaction was statistically significant (p<0.0001). More than half of student daily smokers (53.9%) could be attributed to the combined effect of parent and best friend smoking. The other important feature of the results in this table is the progressive increase in the population attributable risk values with increasing frequency of smoking: from 28.3% for students smoking less than monthly up to 78.7% for those smoking daily. The pattern in Table 4 occurred within each sex, with parental and best friend smoking, separately and together, being significantly (p<0.01) associated with all frequencies of adolescent smoking (data not shown). Table 3. Relative risk, and attributable risk, of a non-smoker having ever experimented with cigarettes Parent smokes Best friend smokes Experimented Relative Risk (95%CI)# Attributable cases Population attributable risk+ Yes N (%)* No N Yes Yes 4553 (66.9%) 2250 2.01 (1.9432.07) 2288 5.4% Yes No 14,742 (45.6%) 17,610 1.52 (1.4931.55) 5043 11.9% No Yes 4098 (54.7%) 3401 1.83 (1.7831.89) 1859 4.4% No No 19,028 (27.6%) 49,858 1.00 - - Total 42,421 73,119 9190 21.7% *Percent of total of each parent-friend smoking category; #Adjusted for age, sex and ethnicity; +Attributable cases / total number of experimenters. Table 4. Relative risk and attributable risk of smoking, associated with smoking by parent and best friend, by frequency of student smoking. Parent smokes Best friend smokes N (%)* in smoking category Relative Risk (95% CI)# Attributable cases Population attributable risk+ Smoking < Monthly Yes Yes 2672 (11.7%) 1.82 (1.7231.93) 1204 9.0% Yes No 3519 (8.7%) 1.41 (1.3431.48) 1023 7.6% No Yes 2665 (15.8%) 2.44 (2.3232.58) 1573 11.7% No No 4589 (5.9%) 1.00 - - Total 13,445 3800 28.3% Monthly smoking Yes Yes 1648 (7.2%) 3.15 (2.9033.42) 1125 18.0% Yes No 1344 (3.3%) 1.54 (1.4331.67) 471 7.5% No Yes 1707 (10.1%) 4.43 (4.1034.79) 1322 21.2% No No 1549 (2.0%) 1.00 - - Total 6248 2918 46.7% Weekly smoking Yes Yes 2321 (10.2%) 5.83 (5.2836.44) 1923 30.7% Yes No 1084 (2.7%) 1.72 (1.5731.89) 454 7.2% No Yes 1821 (10.8%) 6.69 (6.1337.30) 1549 24.7% No No 1035 (1.3%) 1.00 - - Total 6261 3926 62.7% Daily smoking Yes Yes 9361 (41.1%) 14.29 (13.1315.6) 8706 53.9% Yes No 2170 (5.4%) 2.19 (2.0332.36) 1179 7.3% No Yes 3214 (19.0%) 8.25 (7.5738.99) 2824 17.5% No No 1398 (1.8%) 1.00 - - Total 16,143 12,709 78.7% * Percent of total of each parent-friend smoking category; #Adjusted for age, sex and ethnicity; +Attributable cases / total number of smokers in same smoking frequency category. Controlling for smoking in the house greatly reduced the relative risks associated with parental smoking, with this confounding effect weakening with reducing frequency of student smoking. For example, compared to students not exposed to parent nor to best friend smoking, the RR of daily smoking in students exposed to both parent and best friend smoking decreased from 14.49 shown in Table 4 to 9.51 (95%CI: 8.74310.36) with additional adjustment for smoking in the house; while the RR of smoking less than monthly for the same exposure declined from 1.82 in Table 4 to 1.67 (95%CI: 1.5731.79) with additional adjustment for smoking in the house. There was an inverse association between age of starting smoking and frequency of smoking (Table 5). Students who smoked daily were nearly twice as likely to have started smoking by the age of 9 years (18.2%) than students smoking weekly (11.8%) or monthly (10.1%). Table 5. Distribution of age students started smoking monthly, up to 13 years, by current frequency of smoking: 200332005 Age started smoking monthly (years) Smoking frequency

Summary

Abstract

Aim

Compare the effect of parental and best friend smoking across the stages of adolescent smoking, from being a never smoker susceptible to smoking, to being a daily smoker

Method

National cross-sectional annual survey (2002-2006 combined) of 157,637 Year 10 students aged 14 and 15 years who answered an anonymous self-administered questionnaire.

Results

The effects of smoking by parents and best friend varied with stage of adolescent tobacco smoking. Attributable risk calculations showed that parental and best friend smoking explained only 6.3% of susceptibility to smoking among never smokers, and 21.7% of non-smoking students who had ever experimented with cigarettes. The attributable risk for parental and best friend smoking progressively increased with smoking frequency, up to 78.7% for daily smoking. The effect of best friend smoking was stronger than parental smoking, although there was a synergistic effect of both variables on the risk of daily smoking.

Conclusion

Smoking by best friend and parents are strongly associated with current smoking by adolescents, but unrelated to susceptibility to smoke among those who are non-smokers.

Author Information

Acknowledgements

The surveys were carried out by Action on Smoking and Health (ASH), with assistance of the Health Sponsorship Council of New Zealand in 2006. The New Zealand Ministry of Health provided funds.

Correspondence

Assoc Prof Robert Scragg, Epidemiology & Biostatistics, School of Population Health, University of Auckland, Private Bag, Auckland, New Zealand. Fax: +64 (0)9 3737503

Correspondence Email

r.scragg@auckland.ac.nz

Competing Interests

- Mayhew KP, Flay BR, Mott JA. Stages in the development of adolescent smoking. Drug Alcohol Depend 2000;59 Suppl 1:S61-81.-- Chassin L, Presson CC, Pitts SC, Sherman SJ. The natural history of cigarette smoking from adolescence to adulthood in a midwestern community sample: multiple trajectories and their psychosocial correlates. Health Psychol 2000;19(3):223-31.-- Colder CR, Mehta P, Balanda K, et al. Identifying trajectories of adolescent smoking: an application of latent growth mixture modeling. Health Psychol 2001;20(2):127-35.-- Soldz S, Cui X. Pathways through adolescent smoking: a 7-year longitudinal grouping analysis. Health Psychol 2002;21(5):495-504.-- White HR, Pandina RJ, Chen PH. Developmental trajectories of cigarette use from early adolescence into young adulthood. Drug Alcohol Depend 2002;65(2):167-78.-- Audrain-McGovern J, Rodriguez D, Tercyak KP, et al. Identifying and characterizing adolescent smoking trajectories. Cancer Epidemiol Biomarkers Prev 2004;13(12):2023-34.-- Fergusson DM, Horwood LJ. Transitions to cigarette smoking during adolescence. Addict Behav 1995;20(5):627-42.-- Conrad KM, Flay BR, Hill D. Why children start smoking cigarettes: predictors of onset. Br J Addict 1992;87(12):1711-24.-- Flay BR, Hu FB, Siddiqui O, et al. Differential influence of parental smoking and friends' smoking on adolescent initiation and escalation of smoking. J Health Soc Behav 1994;35(3):248-65.-- Flay BR, Hu FB, Richardson J. Psychosocial predictors of different stages of cigarette smoking among high school students. Prev Med 1998;27(5 Pt 3):A9-18.-- Fergusson DM, Lynskey MT, Horwood LJ. The role of peer affiliations, social, family and individual factors in continuities in cigarette smoking between childhood and adolescence. Addiction 1995;90(5):647-59.-- Bauman KE, Carver K, Gleiter K. Trends in parent and friend influence during adolescence: the case of adolescent cigarette smoking. Addict Behav 2001;26(3):349-61.-- Avenevoli S, Merikangas KR. Familial influences on adolescent smoking. Addiction 2003;98 Suppl 1:1-20.-- Scragg R, Laugesen M. Influence of smoking by family and best friend on adolescent tobacco smoking: results from the 2002 New Zealand national survey of year 10 students. Aust N Z J Public Health 2007;31(3):217-23.-- Last JM. A Dictionary of Epidemiology. 4th ed. New York: OUP, 2001.-- Darling N, Cumsille P. Theory, measurement, and methods in the study of family influences on adolescent smoking. Addiction 2003;98 Suppl 1:21-36.-- Kobus K. Peers and adolescent smoking. Addiction 2003;98 Suppl 1:37-55.-- Scragg R. Report of 1999-2006 National Year 10 Smoking Surveys. Auckland: Action on Smoking and Health (ASH), 2007:1-58.-- Pierce JP, Choi WS, Gilpin EA, et al. Validation of susceptibility as a predictor of which adolescents take up smoking in the United States. Health Psychol 1996;15(5):355-61.-- Unger JB, Johnson CA, Stoddard JL, et al. Identification of adolescents at risk for smoking initiation: validation of a measure of susceptibility. Addict Behav 1997;22(1):81-91.-- Rockhill B, Newman B, Weinberg C. Use and misuse of population attributable fractions. Am J Public Health 1998;88(1):15-9.-- Robinson ML, Berlin I, Moolchan ET. Tobacco smoking trajectory and associated ethnic differences among adolescent smokers seeking cessation treatment. J Adolesc Health 2004;35(3):217-24.-- Thomas R, Perera R. School-based programmes for preventing smoking. Cochrane Database of Systematic Reviews, 2006:Issue 3. 1-166. No.: CD001293.-

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