- Email: [email protected]
Do E-cigarettes reduce smoking?
Preventive Medicine 100 (2017) 285–286
Contents lists available at ScienceDirect
Preventive Medicine journal homepage: www.elsevier.com/locate/ypmed
Commentary
Do E-cigarettes reduce smoking? Thomas A. Willsa,⁎, James D. Sargent b a b
Cancer Prevention Program, University of Hawaii Cancer Center, 701 Ilalo Street, Room 528, Honolulu, HI 96816, USA Cancer Control Program, Norris Cotton Cancer Center, Geisel School of Medicine at Dartmouth, Lebanon, NH 03756
A R T IC L E
IN F O
Article history: Received 20 April 2017 Accepted 23 April 2017 Keywords: Young adults E-cigarette Cigarette Dual use
The Doran et al., 2017 study (ref.) addresses how using electronic cigarettes (E-cigarettes) is related to the intensity of smoking combustible cigarettes (cigarettes). The topic is important because E-cigarette use has become prevalent among both adolescents (Singh et al., 2016) and young adults (Wilson and Wang, 2017). It is known from crosssectional studies that a substantial proportion of persons who use Ecigarettes also smoke cigarettes (i.e, dual users: Goniewicz et al., 2016; Pechacek et al., 2016; Wills et al., 2015), but the etiological reasons for this and the consequences of E-cigarette use for public health are still unclear. The public health implications of E-cigarettes will turn on whether their use decreases the net harm that cigarettes and other combustible products cause (Kalkhoran and Glantz, 2015). For near-term gains in public health, cigarette smokers (the ones most at risk for disease) need to completely substitute E-cigarettes for cigarettes; this is because even smoking one or two cigarettes per day greatly increases the risk for disease (Khariwala et al., 2014). Thus E-cigarette use ideally would bring about a significant reduction in cigarettes smoked, through changing the frequency of smoking or the number of cigarettes smoked, and bring users closer to total cessation. For these reasons it is crucial to know whether E-cigarette use brings about a decrease or an increase in smoking. Up to now, however, no studies have addressed in detail how E-cigarette use affects the intensity of cigarette smoking over time. The Doran et al., 2017 study addresses this question with several methodological strengths. The longitudinal study had a large and ethnically diverse sample (391 young-adult smokers from across California) and had repeated assessments of both E-cigarette use and cigarette smoking over an 18-month period. The study had measures for both
⁎ Corresponding author. E-mail addresses: [email protected] (T.A. Wills), [email protected] (J.D. Sargent).
http://dx.doi.org/10.1016/j.ypmed.2017.04.030 0091-7435/© 2017 Elsevier Inc. All rights reserved.
frequency and quantity of smoking, and the researchers used three types of statistical analyses to test whether E-cigarette use was related to decrease or increase in smoking over time. The authors tested for dose-response effects and found that more frequent E-cigarette use was related to greater change in smoking, which strengthens confidence in the findings. Finally, the study included a propensity score to address the possibility that dual users were different from other smokers in ways that might confound the E-cigarette effect on smoking. The basic finding of the Doran et al., 2017 study was consistent across different analytic methods. Though the study was well positioned to determine whether E-cigarette use reduced smoking, the authors found no evidence for this. Instead the results showed that E-cigarette use maintained smoking, or if anything, increased it. Moreover, the effect sizes were substantial. For example, lagged analyses showed that E-cigarette use at one timepoint was related to 40% more cigarettes smoked, and smoking on 18% more days, at the next timepoint. These findings have a number of implications. In this commentary we discuss three issues about the Doran et al., 2017 study. These concern the programmatic implications for preventive medicine; the methodological issues for how relations between Ecigarette use and smoking are most convincingly demonstrated; and the conceptual issue of how dual use can be better understood. Implications for preventive medicine. Doran et al., 2017 found in several analyses that persons who used E-cigarettes showed more smoking over time. This was true for both how often they smoked and for the number of cigarettes they smoked. These provocative findings raise several questions for tobacco control policy. Notably there is the question of whether E-cigarettes are operating to reduce the population burden of tobacco use (and associated disease) or are perhaps increasing it; the present findings tend to support the latter view. Another question is whether there should be consideration of restrictions on E-cigarette use by adults, for example taxation. Advocates for E-cigarettes have resisted calls for taxing E-cigarettes like cigarettes, based on the argument that E-cigarettes help people quit or at least reduce smoking. However recent evidence has been chipping away at these arguments, and if E-cigarette use increases smoking among adults, as it has been demonstrated to do among adolescents (Soneji et al., 2017), then public health officials and legislators may have to grapple with his question. Methodological issues. The methodological issue revolves around how an effect for E-cigarettes can be tested most convincingly. The Doran et al., 2017 study gets at this issue in two different ways. One approach was by examining the relation between E-cigarette use and smoking over different prediction intervals: (a) by examining the relation of prior E-cigarette use (over the 6 months before study outset)
286
T.A. Wills, J.D. Sargent / Preventive Medicine 100 (2017) 285–286
to total cigarette consumption over the study period; (b) by testing how stability of E-cigarette use over the five repeated assessments was related to total cigarette consumption over the study period; and (c) by utilizing the repeated measures to test how E-cigarette use at one time point was related to smoking at an assessment 3 months later. In all cases there was a significant positive effect, with initial level (or stability) of E-cigarette use related to a higher level of smoking at the criterion point. Thus it is clear that E-cigarette use is related to a higher level of smoking over time. However, it could still be argued that there was a pre-existing vulnerability that made some participants more likely to use E-cigarettes and also more likely to smoke. Researchers typically deal with this question by obtaining a measure of the proposed vulnerability and testing whether an effect of the predictor still occurs when the influence of the vulnerability factor on E-cigarette use and smoking is removed statistically. Doran et al., 2017 did this with a propensity score (i.e., combining several variables that all predicted likelihood of smoking) and found that E-cigarettes were related to increased smoking independent of the propensity score. Other researchers have implemented similar procedures in studies of smoking onset, for example by controlling for susceptibility to smoking (Barrington-Trimis et al., 2016; Primack et al., 2015) or conducting compound analyses that control for variables such juvenile delinquency or impulsiveness and risktaking tendency (Leventhal et al., 2015; Wills et al., 2017), and have found E-cigarettes are related to smoking onset independent of these vulnerability measures. Thus the argument that the findings are due to some underlying vulnerability has been considerably weakened and the most parsimonious conclusion is that E-cigarette use operates to increase smoking. It would still be desirable to have a control variable that explicitly tapped nicotine dependence, as it might be that persons who were more addicted to nicotine used E-cigarettes and also smoked more cigarettes. This possibility was not directly addressed by the Doran et al., 2017 study and should be tested in further research. How does dual use occur? But what does dual use really mean, and how do E-cigarettes work to maintain or increase smoking rather than reduce it? A firm answer is not available at this time but some suggestions have been made from different perspectives. One is that Ecigarettes activate some of the same behavioral script as cigarettes (inhaling and exhaling a cloud of smoke) so simple physical sensations may be at work. A second is that using an E-cigarette may highlight sensory aspects of cigarettes (e.g., taste, relaxation) and thus increase positive expectancies about what cigarettes will do (Pokhrel et al., 2014b; Wills et al., 2016), thus encouraging higher rates of use. Social aspects may be important because E-cigarette users may naturally be attracted to peer groups that include cigarette smokers, as they share certain psychological attributes (Kristjansson et al., 2015; Leventhal et al., 2016), and this would tend to encourage more frequent smoking. Also, nicotine is a highly addictive substance and E-cigarette users who need a stronger “hit” (Primack et al., 2015) may be inclined to add cigarettes to their diet so as to get a stronger dose or fill in periods when smoking is impractical (e.g., because of indoor air regulations). While a start has been made in qualitative research (Pokhrel et al., 2014a), we still lack a detailed picture of how E-cigarette use occurs on a daily level: what are the situations where E-cigarettes precede or follow cigarette smoking, is the social context the same, are the motivations the same (e.g., socializing, stress reduction, addiction), and are they with the same people or with different groups of users.
In conclusion, we have noted that the Doran et al., 2017 study provides a fairly convincing demonstration that E-cigarette use increases the frequency and quantity of cigarette smoking. It has some possible limitations in that the sample was nondaily smokers and the findings should be replicated in other populations, such as moderate smokers. However the results parallel studies of onset conducted with several different sampling methods (Soneji et al., 2017) and the study raises useful questions about the mechanism(s) through which E-cigarette use affects intensity of smoking. From a prevention standpoint, the findings point to a rationale for educating the public about possible risks of Ecigarette use, as well as possible benefits, in public health approaches to reduce or eliminate smoking (U.S. Department of Health and Human Services, 2016). References Barrington-Trimis, J.L., Urman, R., Berhane, K., et al., 2016. E-cigarettes and future cigarette use. Pediatrics 138, e20160379. Doran, N., Brikmanis, K., Petersen, A., Delucchi, K., Al-Delaimy, W.K., Luczak, S., Myers, M., Strong, D., 2017. Does e-cigarette use predict cigarette escalation? A longitudinal study of young adult non-daily smokers. Prev. Med. 100, 279–284. Goniewicz, M.L., Leigh, N.J., Gawron, M., Nadolska, J., Balwicki, L., McGuire, C., Sobczak, A., 2016. Dual use of electronic and tobacco cigarettes among adolescents: a cross-sectional study in Poland. Int. J. Public Health 61, 189–197. Kalkhoran, S., Glantz, S.A., 2015. Modeling the health effects of expanding e-cigarette sales in the United States and United Kingdom: a Monte Carlo analysis. JAMA Intern. Med. 75, 1671–1680. Khariwala, S.S., Scheuermann, T.S., Berg, C.J., et al., 2014. Cotinine and tobacco-specific carcinogen exposure among nondaily smokers in a multiethnic sample. Nicotine Tob. Res. 16, 600–605. Kristjansson, A.L., Mann, M.J., Sigfusdottir, I.D., 2015. Licit and illicit substance use by adolescent e-cigarette users compared with conventional cigarette smokers, dual users, and nonusers. J. Adolesc. Health 57, 562–564. Leventhal, A.M., Strong, D.R., Kirkpatrick, M.G., Unger, J.B., et al., 2015. Association of electronic cigarette use with initiation of combustible tobacco smoking in early adolescence. JAMA 314, 700–707. Leventhal, A.M., Strong, D.R., Sussman, S., et al., 2016. Psychiatric comorbidity in adolescent electronic and conventional cigarette use. J. Psychiatr. Res. 73, 71–78. Pechacek, T.F., Nayak, P., Gregory, K.R., Weaver, S.R., Eriksen, M.P., 2016. The potential that electronic nicotine delivery systems can be a disruptive technology: results from a national survey. Nicotine Tob. Res. 18, 1989–1997. Pokhrel, P., Herzog, T.A., Muranaka, N., Regmi, S., Fagan, P., 2014a. Contexts of cigarette and e-cigarette use among dual users: a qualitative study. BMC Public Health 15, 859. Pokhrel, P., Little, M.A., Fagan, P., Muranaka, N., Herzog, T.A., 2014b. Electronic cigarette use outcome expectancies among college students. Addict. Behav. 39, 1062–1065. Primack, B.A.S., Soneji, S., Stoolmiller, M., Fine, M.J., Sargent, J.D., 2015. Progression to traditional cigarette smoking after electronic cigarette use among US adolescents and young adults. JAMA Pediatr. 169, 1018–1023. Singh, T., Arrazola, R.E., Corey, C.G., et al., 2016. Tobacco use among middle and high school students– United States, 2011-2015. MMWR Morb. Mortal. Wkly Rep. 65, 362–367. Soneji, S., Barrington-Trimis, J., Wills, T.A., et al., 2017. E-cigarette use and subsequent cigarette smoking among adolescents and young adults: a systematic review and metaanalysis. JAMA Pediatr. (in press). U.S. Department of Health and Human Services, 2016. E-cigarette use Among Youth and Young Adults: a Report of the Surgeon General. 23. U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Chronic Disease Prevention and Health Promotion, Office on Smoking and Health, Atlanta, GA. Wills, T.A., Gibbons, F.X., Sargent, J.D., Schweitzer, R.J., 2016. How is the effect of e-cigarette use on smoking onset mediated: a longitudinal analysis. Psychol. Addict. Behav. 30, 876–886. Wills, T.A., Knight, R., Williams, R., et al., 2015. Risk factors for exclusive e-cigarette use and dual e-cigarette and tobacco use in adolescents. Pediatrics 135, e43–e51. Wills, T.A., Knight, R., Sargent, J.D., Gibbons, F.X., Pagano, I., Williams, R.J., 2017. Longitudinal study of e-cigarette use and cigarette smoking onset among high school students in Hawaii. Tob. Control. 26, 34–39. Wilson, F.A., Wang, Y., 2017. Recent findings on the prevalence of e-cigarette use among adults in the US. Am. J. Prev. Med. 52, 385–390.
Contents lists available at ScienceDirect
Preventive Medicine journal homepage: www.elsevier.com/locate/ypmed
Commentary
Do E-cigarettes reduce smoking? Thomas A. Willsa,⁎, James D. Sargent b a b
Cancer Prevention Program, University of Hawaii Cancer Center, 701 Ilalo Street, Room 528, Honolulu, HI 96816, USA Cancer Control Program, Norris Cotton Cancer Center, Geisel School of Medicine at Dartmouth, Lebanon, NH 03756
A R T IC L E
IN F O
Article history: Received 20 April 2017 Accepted 23 April 2017 Keywords: Young adults E-cigarette Cigarette Dual use
The Doran et al., 2017 study (ref.) addresses how using electronic cigarettes (E-cigarettes) is related to the intensity of smoking combustible cigarettes (cigarettes). The topic is important because E-cigarette use has become prevalent among both adolescents (Singh et al., 2016) and young adults (Wilson and Wang, 2017). It is known from crosssectional studies that a substantial proportion of persons who use Ecigarettes also smoke cigarettes (i.e, dual users: Goniewicz et al., 2016; Pechacek et al., 2016; Wills et al., 2015), but the etiological reasons for this and the consequences of E-cigarette use for public health are still unclear. The public health implications of E-cigarettes will turn on whether their use decreases the net harm that cigarettes and other combustible products cause (Kalkhoran and Glantz, 2015). For near-term gains in public health, cigarette smokers (the ones most at risk for disease) need to completely substitute E-cigarettes for cigarettes; this is because even smoking one or two cigarettes per day greatly increases the risk for disease (Khariwala et al., 2014). Thus E-cigarette use ideally would bring about a significant reduction in cigarettes smoked, through changing the frequency of smoking or the number of cigarettes smoked, and bring users closer to total cessation. For these reasons it is crucial to know whether E-cigarette use brings about a decrease or an increase in smoking. Up to now, however, no studies have addressed in detail how E-cigarette use affects the intensity of cigarette smoking over time. The Doran et al., 2017 study addresses this question with several methodological strengths. The longitudinal study had a large and ethnically diverse sample (391 young-adult smokers from across California) and had repeated assessments of both E-cigarette use and cigarette smoking over an 18-month period. The study had measures for both
⁎ Corresponding author. E-mail addresses: [email protected] (T.A. Wills), [email protected] (J.D. Sargent).
http://dx.doi.org/10.1016/j.ypmed.2017.04.030 0091-7435/© 2017 Elsevier Inc. All rights reserved.
frequency and quantity of smoking, and the researchers used three types of statistical analyses to test whether E-cigarette use was related to decrease or increase in smoking over time. The authors tested for dose-response effects and found that more frequent E-cigarette use was related to greater change in smoking, which strengthens confidence in the findings. Finally, the study included a propensity score to address the possibility that dual users were different from other smokers in ways that might confound the E-cigarette effect on smoking. The basic finding of the Doran et al., 2017 study was consistent across different analytic methods. Though the study was well positioned to determine whether E-cigarette use reduced smoking, the authors found no evidence for this. Instead the results showed that E-cigarette use maintained smoking, or if anything, increased it. Moreover, the effect sizes were substantial. For example, lagged analyses showed that E-cigarette use at one timepoint was related to 40% more cigarettes smoked, and smoking on 18% more days, at the next timepoint. These findings have a number of implications. In this commentary we discuss three issues about the Doran et al., 2017 study. These concern the programmatic implications for preventive medicine; the methodological issues for how relations between Ecigarette use and smoking are most convincingly demonstrated; and the conceptual issue of how dual use can be better understood. Implications for preventive medicine. Doran et al., 2017 found in several analyses that persons who used E-cigarettes showed more smoking over time. This was true for both how often they smoked and for the number of cigarettes they smoked. These provocative findings raise several questions for tobacco control policy. Notably there is the question of whether E-cigarettes are operating to reduce the population burden of tobacco use (and associated disease) or are perhaps increasing it; the present findings tend to support the latter view. Another question is whether there should be consideration of restrictions on E-cigarette use by adults, for example taxation. Advocates for E-cigarettes have resisted calls for taxing E-cigarettes like cigarettes, based on the argument that E-cigarettes help people quit or at least reduce smoking. However recent evidence has been chipping away at these arguments, and if E-cigarette use increases smoking among adults, as it has been demonstrated to do among adolescents (Soneji et al., 2017), then public health officials and legislators may have to grapple with his question. Methodological issues. The methodological issue revolves around how an effect for E-cigarettes can be tested most convincingly. The Doran et al., 2017 study gets at this issue in two different ways. One approach was by examining the relation between E-cigarette use and smoking over different prediction intervals: (a) by examining the relation of prior E-cigarette use (over the 6 months before study outset)
286
T.A. Wills, J.D. Sargent / Preventive Medicine 100 (2017) 285–286
to total cigarette consumption over the study period; (b) by testing how stability of E-cigarette use over the five repeated assessments was related to total cigarette consumption over the study period; and (c) by utilizing the repeated measures to test how E-cigarette use at one time point was related to smoking at an assessment 3 months later. In all cases there was a significant positive effect, with initial level (or stability) of E-cigarette use related to a higher level of smoking at the criterion point. Thus it is clear that E-cigarette use is related to a higher level of smoking over time. However, it could still be argued that there was a pre-existing vulnerability that made some participants more likely to use E-cigarettes and also more likely to smoke. Researchers typically deal with this question by obtaining a measure of the proposed vulnerability and testing whether an effect of the predictor still occurs when the influence of the vulnerability factor on E-cigarette use and smoking is removed statistically. Doran et al., 2017 did this with a propensity score (i.e., combining several variables that all predicted likelihood of smoking) and found that E-cigarettes were related to increased smoking independent of the propensity score. Other researchers have implemented similar procedures in studies of smoking onset, for example by controlling for susceptibility to smoking (Barrington-Trimis et al., 2016; Primack et al., 2015) or conducting compound analyses that control for variables such juvenile delinquency or impulsiveness and risktaking tendency (Leventhal et al., 2015; Wills et al., 2017), and have found E-cigarettes are related to smoking onset independent of these vulnerability measures. Thus the argument that the findings are due to some underlying vulnerability has been considerably weakened and the most parsimonious conclusion is that E-cigarette use operates to increase smoking. It would still be desirable to have a control variable that explicitly tapped nicotine dependence, as it might be that persons who were more addicted to nicotine used E-cigarettes and also smoked more cigarettes. This possibility was not directly addressed by the Doran et al., 2017 study and should be tested in further research. How does dual use occur? But what does dual use really mean, and how do E-cigarettes work to maintain or increase smoking rather than reduce it? A firm answer is not available at this time but some suggestions have been made from different perspectives. One is that Ecigarettes activate some of the same behavioral script as cigarettes (inhaling and exhaling a cloud of smoke) so simple physical sensations may be at work. A second is that using an E-cigarette may highlight sensory aspects of cigarettes (e.g., taste, relaxation) and thus increase positive expectancies about what cigarettes will do (Pokhrel et al., 2014b; Wills et al., 2016), thus encouraging higher rates of use. Social aspects may be important because E-cigarette users may naturally be attracted to peer groups that include cigarette smokers, as they share certain psychological attributes (Kristjansson et al., 2015; Leventhal et al., 2016), and this would tend to encourage more frequent smoking. Also, nicotine is a highly addictive substance and E-cigarette users who need a stronger “hit” (Primack et al., 2015) may be inclined to add cigarettes to their diet so as to get a stronger dose or fill in periods when smoking is impractical (e.g., because of indoor air regulations). While a start has been made in qualitative research (Pokhrel et al., 2014a), we still lack a detailed picture of how E-cigarette use occurs on a daily level: what are the situations where E-cigarettes precede or follow cigarette smoking, is the social context the same, are the motivations the same (e.g., socializing, stress reduction, addiction), and are they with the same people or with different groups of users.
In conclusion, we have noted that the Doran et al., 2017 study provides a fairly convincing demonstration that E-cigarette use increases the frequency and quantity of cigarette smoking. It has some possible limitations in that the sample was nondaily smokers and the findings should be replicated in other populations, such as moderate smokers. However the results parallel studies of onset conducted with several different sampling methods (Soneji et al., 2017) and the study raises useful questions about the mechanism(s) through which E-cigarette use affects intensity of smoking. From a prevention standpoint, the findings point to a rationale for educating the public about possible risks of Ecigarette use, as well as possible benefits, in public health approaches to reduce or eliminate smoking (U.S. Department of Health and Human Services, 2016). References Barrington-Trimis, J.L., Urman, R., Berhane, K., et al., 2016. E-cigarettes and future cigarette use. Pediatrics 138, e20160379. Doran, N., Brikmanis, K., Petersen, A., Delucchi, K., Al-Delaimy, W.K., Luczak, S., Myers, M., Strong, D., 2017. Does e-cigarette use predict cigarette escalation? A longitudinal study of young adult non-daily smokers. Prev. Med. 100, 279–284. Goniewicz, M.L., Leigh, N.J., Gawron, M., Nadolska, J., Balwicki, L., McGuire, C., Sobczak, A., 2016. Dual use of electronic and tobacco cigarettes among adolescents: a cross-sectional study in Poland. Int. J. Public Health 61, 189–197. Kalkhoran, S., Glantz, S.A., 2015. Modeling the health effects of expanding e-cigarette sales in the United States and United Kingdom: a Monte Carlo analysis. JAMA Intern. Med. 75, 1671–1680. Khariwala, S.S., Scheuermann, T.S., Berg, C.J., et al., 2014. Cotinine and tobacco-specific carcinogen exposure among nondaily smokers in a multiethnic sample. Nicotine Tob. Res. 16, 600–605. Kristjansson, A.L., Mann, M.J., Sigfusdottir, I.D., 2015. Licit and illicit substance use by adolescent e-cigarette users compared with conventional cigarette smokers, dual users, and nonusers. J. Adolesc. Health 57, 562–564. Leventhal, A.M., Strong, D.R., Kirkpatrick, M.G., Unger, J.B., et al., 2015. Association of electronic cigarette use with initiation of combustible tobacco smoking in early adolescence. JAMA 314, 700–707. Leventhal, A.M., Strong, D.R., Sussman, S., et al., 2016. Psychiatric comorbidity in adolescent electronic and conventional cigarette use. J. Psychiatr. Res. 73, 71–78. Pechacek, T.F., Nayak, P., Gregory, K.R., Weaver, S.R., Eriksen, M.P., 2016. The potential that electronic nicotine delivery systems can be a disruptive technology: results from a national survey. Nicotine Tob. Res. 18, 1989–1997. Pokhrel, P., Herzog, T.A., Muranaka, N., Regmi, S., Fagan, P., 2014a. Contexts of cigarette and e-cigarette use among dual users: a qualitative study. BMC Public Health 15, 859. Pokhrel, P., Little, M.A., Fagan, P., Muranaka, N., Herzog, T.A., 2014b. Electronic cigarette use outcome expectancies among college students. Addict. Behav. 39, 1062–1065. Primack, B.A.S., Soneji, S., Stoolmiller, M., Fine, M.J., Sargent, J.D., 2015. Progression to traditional cigarette smoking after electronic cigarette use among US adolescents and young adults. JAMA Pediatr. 169, 1018–1023. Singh, T., Arrazola, R.E., Corey, C.G., et al., 2016. Tobacco use among middle and high school students– United States, 2011-2015. MMWR Morb. Mortal. Wkly Rep. 65, 362–367. Soneji, S., Barrington-Trimis, J., Wills, T.A., et al., 2017. E-cigarette use and subsequent cigarette smoking among adolescents and young adults: a systematic review and metaanalysis. JAMA Pediatr. (in press). U.S. Department of Health and Human Services, 2016. E-cigarette use Among Youth and Young Adults: a Report of the Surgeon General. 23. U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Chronic Disease Prevention and Health Promotion, Office on Smoking and Health, Atlanta, GA. Wills, T.A., Gibbons, F.X., Sargent, J.D., Schweitzer, R.J., 2016. How is the effect of e-cigarette use on smoking onset mediated: a longitudinal analysis. Psychol. Addict. Behav. 30, 876–886. Wills, T.A., Knight, R., Williams, R., et al., 2015. Risk factors for exclusive e-cigarette use and dual e-cigarette and tobacco use in adolescents. Pediatrics 135, e43–e51. Wills, T.A., Knight, R., Sargent, J.D., Gibbons, F.X., Pagano, I., Williams, R.J., 2017. Longitudinal study of e-cigarette use and cigarette smoking onset among high school students in Hawaii. Tob. Control. 26, 34–39. Wilson, F.A., Wang, Y., 2017. Recent findings on the prevalence of e-cigarette use among adults in the US. Am. J. Prev. Med. 52, 385–390.