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• Response to Dr. Glantz
  David T Levy, Kenneth Warner, K. Michael Cummings, David Hammond, Geoffrey Fong, James T. Thrasher, Maciej Goniewicz and Ronald Borland
  Published on: 28 October 2019
• The reality may not be linear
  Stanton A Glantz
  Published on: 28 October 2019

• Published on: 28 October 2019

  Response to Dr. Glantz

  • David T Levy, Professor Georgetown University
  • Other Contributors:
    • Kenneth Warner, Professor
    • K. Michael Cummings, Professor
    • David Hammond, Professor
    • Geoffrey Fong, Professor
    • James T. Thrasher, Professor
    • Maciej Goniewicz, Professor
    • Ronald Borland, Professor

  NOT PEER REVIEWED
  We would like to clear up some misconceptions in Dr. Glantz’s reply to our recent article (1). First, our analytic approach did not assume linearity as the title of Dr. Glantz’s response implies. On the contrary, we applied a log linear form, which not only better fit the data, but also incorporates non-linearities. Additionally, we also conducted and provided results using a linear form in the supplementary material, which yielded similar results.

  In his reply to our paper, Dr. Glantz claims that we should have started the vaping period in 2009 rather than in 2014 or 2013. However, we feel this criticism is wrong since we provided extensive data in the paper showing that vaping among youth was minimal until at least 2013.
  Consequently, we focused on when vaping became more widespread and, by most accounts, became a concern. Further, we conducted analyses that considered changes in trend for other years and obtained qualitatively similar results when the transition was specified as dating back to 2013 or 2012. We also conducted analyses which allowed for changes in trend in both 2009 and 2014 and found no change in trend from 2009 onward, whereas the change in trend from 2014 onward continued to hold. We understand that Dr. Glantz and colleagues in another paper (2) used 2009 as a base year for vaping. However, we feel this choice was a poor one since virtually no students were using e-cigarettes in 2009, and hence vaping would not be...

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  NOT PEER REVIEWED
  We would like to clear up some misconceptions in Dr. Glantz’s reply to our recent article (1). First, our analytic approach did not assume linearity as the title of Dr. Glantz’s response implies. On the contrary, we applied a log linear form, which not only better fit the data, but also incorporates non-linearities. Additionally, we also conducted and provided results using a linear form in the supplementary material, which yielded similar results.

  In his reply to our paper, Dr. Glantz claims that we should have started the vaping period in 2009 rather than in 2014 or 2013. However, we feel this criticism is wrong since we provided extensive data in the paper showing that vaping among youth was minimal until at least 2013.
  Consequently, we focused on when vaping became more widespread and, by most accounts, became a concern. Further, we conducted analyses that considered changes in trend for other years and obtained qualitatively similar results when the transition was specified as dating back to 2013 or 2012. We also conducted analyses which allowed for changes in trend in both 2009 and 2014 and found no change in trend from 2009 onward, whereas the change in trend from 2014 onward continued to hold. We understand that Dr. Glantz and colleagues in another paper (2) used 2009 as a base year for vaping. However, we feel this choice was a poor one since virtually no students were using e-cigarettes in 2009, and hence vaping would not be a factor influencing adolescent smoking.

  Dr. Glantz also criticizes our study by pointing out several years during the vaping period when smoking prevalence did not decline. While it is true that smoking did not decline in some years during the vaping period, exceptions do not prove the rule. Indeed, the point of statistical analysis is to distinguish salient trends. Our aim was to provide straightforward analyses of the trends in cigarette smoking replicated across six different surveys. We estimated equations which allowed for long-term trends and changes in trend, and corrected for autocorrelation in the error terms where tests indicated a problem. Across six separate surveys, we obtained remarkably consistent results showing that the downward trend in smoking rates were greatly accelerated since vaping became more widespread.

  In his criticism of our study Dr. Glantz focused particular attention on our results from the NYTS. We began our analysis of these data in 2011 because data became publicly available on an annual basis beginning in that year. Further, these data show that, while high school smoking rates fell from 15.8% to 12.7% between 2011 and 2013, representing a 20% drop in that three-year period, smoking rates declined to 9.8% in 2014 representing a 25% decline in just one year. Smoking prevalence further declined to 7.6% in 2017, representing a 40% drop since 2013. Nonetheless, the NYTS data provides the weakest indication of the change in trend during the vaping period due to the limited ability to detect pre-vaping trends.

  Since our study was completed, more recent data have been published on youth and young adult smoking and vaping. In particular, the just released Monitoring the Future data indicate that last 30 day prevalence of smoking by 12th graders fell from 9.7% in 2017 to 7.6% in 2018, a 22% drop in just one year. In addition, NHIS data indicate that smoking prevalence for 18-24 year olds (both genders) fell from 13.1% in 2016 to 10.4% in 2017, a 21% drop in one year. These new data are consistent with the trends we describe in our paper.

  Finally, we disagree in three ways with Dr. Glantz’s criticism that our paper only narrowly focused on cigarette use while ignoring total tobacco product use, including e-cigarettes. First, our decision to focus on the associations between e-cigarettes and cigarettes was based on concerns that e-cigarette use leads to increased smoking (3). Second, we think it is inappropriate to combine e-cigarettes and cigarettes in the same category of health risk, since virtually all scholarly evidence reviews have concluded that e-cigarettes are likely substantially less harmful than cigarettes and other combustible tobacco products, including the NASEM (3), PHE (4), and RCP (5) reports. Third, despite FDA’s legal classification of e-cigarettes as tobacco products, a strong argument can be made that e-cigarettes are not tobacco products at all, but rather a specific type of nicotine delivery product, just as nicotine patches, gum, and lozenges are also nicotine delivery products. No one would classify nicotine patches, gum, and lozenges as tobacco products. Indeed, classifying e-cigarettes as tobacco is the reason that Dr. Glantz can make his final claim that total tobacco use has risen with the introduction of e-cigarettes. While this conclusion is true under the classification scheme that Dr. Glantz uses, it is irrelevant to the arguments we made. Our arguments hinge on whether the increase in vaping is offset by a greater decrease in smoking (and other tobacco use) than would be expected in a world without e-cigarettes. We have never suggested better than one for one substitution, and would agree that vaping has substantially increased.

  The data presented by Dr. Glantz on e-cigarette use are based on any last 30 day use. An important advance in our study over prior analyses, including the earlier study by Dr. Glantz and colleagues (2), was that we also considered measures of more established use, such as having smoked 100 cigarettes, daily smoking and smoking half a pack a day. These are more valid measures of regular smoking and are thus more directly related to public health impacts. Our study found that the conclusions about trends in vaping and smoking were robust across different measures of smoking. Indeed, we considered the ratio of daily to last 30 day smoking as an indicator of transitions from experimental to more regular cigarette smoking. We again found more rapidly declining rates during the period after vaping became more widespread.

  It will be important to carefully monitor trends in the use of cigarettes, e-cigarettes and other nicotine delivery products to inform the kinds of policies that are likely to yield beneficial health outcomes for the population.

  References
  (1) Levy DT, Warner KE, Cummings KM, et al., Examining the relationship of vaping to smoking initiation among US youth and young adults: a reality check. Tob Control. 2018 Nov 20. pii: tobaccocontrol-2018-054446. doi: 10.1136/tobaccocontrol-2018-054446. [Epub ahead of print]

  (2) Dutra L, Glantz S. E-cigarettes and national adolescent cigarette use: 2004-2014. Pediatrics. 2017 Feb;139(2). pii: e20162450. doi: 10.1542/peds.2016-2450.

  (3) National Academy of Sciences Engineering and Medicine. Public health consequences of e-cigarettes. Washington, DC: The National Academies Press, 2018.

  (4) Public Health England. E-cigarettes and vaping: policy, regulation and guidance. London: PHE;2018.

  (5) Royal College of Physicians. Nicotine without smoke: Tobacco harm reduction. London: RCP;2016.

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  Conflict of Interest:
  None declared.

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• Published on: 28 October 2019

  The reality may not be linear

  • Stanton A Glantz, Professor of Medicine Universiy of California San Francisco

  NOT PEER REVIEWED
  David Levy and colleagues’ paper “Examining the relationship of vaping to smoking initiation among US youth and young adults: a reality check” used data from all the surveys over time that measured youth and young adult e-cigarette use and smoking and concluded there was a substantial increase in youth vaping prevalence beginning in about 2014. Time trend analyses showed that the decline in past 30-day smoking prevalence accelerated by two to four times after 2014. Indicators of more established smoking rates, including the proportion of daily smokers among past 30-day smokers, also decreased more rapidly as vaping became more prevalent.

  The inverse relationship between vaping and smoking was robust across different data sets for both youth and young adults and for current and more established smoking. While trying electronic cigarettes may causally increase smoking among some youth, the aggregate effect at the population level appears to be negligible given the reduction in smoking initiation during the period of vaping's ascendance.

  The good news is that Levy and colleagues are finally accepting the overwhelming evidence that kids who start with e-cigarettes are more likely to end up smoking cigarettes, the so-called “gateway effect.”

  Now they have fallen back to arguing that the gateway effect is not big enough to overcome the benefits of e-cigs as substitutes for cigarettes.

  The approach they used, interrupted ti...

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  NOT PEER REVIEWED
  David Levy and colleagues’ paper “Examining the relationship of vaping to smoking initiation among US youth and young adults: a reality check” used data from all the surveys over time that measured youth and young adult e-cigarette use and smoking and concluded there was a substantial increase in youth vaping prevalence beginning in about 2014. Time trend analyses showed that the decline in past 30-day smoking prevalence accelerated by two to four times after 2014. Indicators of more established smoking rates, including the proportion of daily smokers among past 30-day smokers, also decreased more rapidly as vaping became more prevalent.

  The inverse relationship between vaping and smoking was robust across different data sets for both youth and young adults and for current and more established smoking. While trying electronic cigarettes may causally increase smoking among some youth, the aggregate effect at the population level appears to be negligible given the reduction in smoking initiation during the period of vaping's ascendance.

  The good news is that Levy and colleagues are finally accepting the overwhelming evidence that kids who start with e-cigarettes are more likely to end up smoking cigarettes, the so-called “gateway effect.”

  Now they have fallen back to arguing that the gateway effect is not big enough to overcome the benefits of e-cigs as substitutes for cigarettes.

  The approach they used, interrupted time series analysis, estimates the declining trend in cigarette use over time, then tests whether this trend changes (in this case, they generally tested for a slope change) after the advent of e-cigarettes.

  Interrupted time series is a well-established method for analyzing changes in trends. Indeed Lauren Dutra and I (1) used interrupted time series to do a similar analysis of the effect that the advent of e-cigarettes had on cigarette smoking among youth using the National Youth Tobacco Survey from 2004 to 2014. Based on data over that time, we found that the advent of e-cigarettes (using a start date of 2009 for e-cigs) did not affect the declining trend in cigarette smoking, but led to an increase in total tobacco product use (Figure 1 in our paper).
  Lauren and I also used individual-level data (something Levy and colleagues did not consider in their analysis) and found that about one-third of the kids using e-cigarettes had risk profiles that made them unlikely to start using nicotine with conventional cigarettes. Thus, e-cigarettes are expanding the tobacco market.

  Levy and colleagues expand the time period of analysis up to 2016 or 2017 (depending on the data source). This is an important addition because, as they note, e-cigarette use has continued to grow since 2014 (their Figure 1).

  I have several concerns about the analysis and interpretation of the data that Levy and colleagues present.

  The assumption in interrupted time series analysis as they (and we) do it is that the underlying trend is linear (a straight line). The figures in the supplementary file suggest that many of the time histories are curved. Failing to account for this curvature can distort the results and also make the results highly sensitive to the break year (i.e., where the line bends) in the analysis.

  A related concern because of the curvature in the data is that the break year they use in their analysis is 2014. They justify this by arguing that 2014 is when e-cigarette use took off. But, if you look at their Figure 1, you could also argue for using 2009 as the break year because that is where the data they have on e-cig use extrapolated back to zero. While e-cig use was lower before 2014, an increasing effect of e-cigs would be captured in the slope change in an interrupted time series model (assuming that the linear assumption is met).

  The specific shape of the data curve is especially important in most recent years where e-cigarette use has increased so much among youth and young adults. This fact, combined with the gateway effect, would lead one to predict that historical drops in cigarette smoking would stop or even reverse. Indeed, looking at the detailed data in the supplementary figures shows this in several (but not all) cases:

  • The Monitoring the Future (MTF) data showed increases in 10th grade 30 day and daily cigarette smoking (Supplementary Figures 1 and 8) and essentially flat 12th grade smoking between 2016 and 2017 (Supplementary Figure 2).

  • The National Youth Tobacco Survey showed flat 30 day cigarette smoking from 2014 to 2017 (Supplementary Figure 3), the first time that there was not a drop in cigarette smoking since NYTS started in 2004. (I also do not understand why Levy and colleagues did not use the NYTS back to 2004; they started in 2011.)

  • The National Health Interview Survey showed flat young adult smoking prevalence from 2015 to 2016 for both males and females (Supplementary Figures 13 and 14).
  Another important omission in Levy and colleagues’ paper is that they only present data on cigarette smoking rather than total tobacco product use. This is an exceptionally important variable because if e-cigarettes are increasing nicotine use among youth, that is a bad thing.
  And that is what Lauren Dutra and I found through 2014 (figure above). The rapid increase in e -cigarette use after 2014 in Levy’s Figure 1 reinforces this concern.

  New data for 2018 released by the CDC in the November 16, 2018 MMWR (2) reinforces how serious this problem is. They documented continuing increases in e-cigarette use through 2018 (figure in MMWR) and, more important, increases in any tobacco use.

  That is the real reality.

  REFERENCES

  (1) Dutra L, Glantz S. E-cigarettes and National Adolescent Cigarette Use: 2004-2014. Pediatrics. 2017 Feb;139(2). pii: e20162450. doi: 10.1542/peds.2016-2450.
  (2) Cullen KA, Ambrose BK, Gentzke AS, Apelberg BJ, Jamal A, King BA. Notes from the Field: Use of Electronic Cigarettes and Any Tobacco Product Among Middle and High School Students — United States, 2011–2018. MMWR Morb Mortal Wkly Rep 2018;67:1276–1277. DOI: http://dx.doi.org/10.15585/mmwr.mm6745a5

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  Conflict of Interest:
  None declared.

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