On 2016 Nov 22, Peter Hajek commented:

Thank you Laurie for looking into this and confirming that the data do not suggest that vaping undermines quitting. Regarding a possible benefit of vaping, a better test would be including participants who were smoking at 3M, as you did, but compare those who did and those who did not try vaping BETWEEN the 3M and 6M follow-up. This is because those still smoking and reporting using EC prior to the 3M f-u are self-selected for not benefiting from vaping (up to that point anyway). Doing it the way suggested above avoids some of that problem - but the result would remain affected by self-selection and uncertainty about the purpose and intensity of e-cig use. Thanks again, Peter

On 2016 Nov 21, Laurie Zawertailo commented:

We thank Dr. Hajek for his constructive criticism of our paper and his suggested alternate analysis. We agree that smokers reporting e-cigarette use at follow-up may have been less likely to be able to quit using the standard treatment offered and so may have resorted to e-cigarettes to aid in their quit attempt. We were able to conduct the suggested analysis by looking at smokers who were not quit at the 3-month follow-up time point (i.e. failed on the initial treatment, n=1626). At the 6-month follow-up we assessed whether or not they reported being quit and whether or not they had used e-cigarettes. At 6-month follow-up, 11.4% of e-cigarette non-users reported quit (7-day PPA), compared to 9.2% of e-cigarette users (p=0.24, NS). Therefore, there is no evidence to support Dr. Hajek’s hypothesis that e-cigarette use will increase quit rates among those who do not quit smoking using standard evidence-based treatment (NRT plus counselling). Again these data are limited due to the lack of information regarding dose and duration of e-cigarette use and due to bias caused by self-selection.

On 2016 Sep 27, Peter Hajek commented:

The conclusion is mistaken. People who failed in their initial attempt to quit smoking with NRT would be much more likely to try alternatives than those who quit successfully. The finding that non-EC use group did better is an artifact of this - treatment successes were concentrated there. It would be more informative to look at people who failed with the initial treatment and compare those who did and those who did not try e-cigarettes during the follow-up period. Such a comparison may well show that e-cigarette use had a positive effect. Self-selection would remain a problem, but perhaps the authors could check this?

On 2016 Sep 27, Peter Hajek commented:

The conclusion is mistaken. People who failed in their initial attempt to quit smoking with NRT would be much more likely to try alternatives than those who quit successfully. The finding that non-EC use group did better is an artifact of this - treatment successes were concentrated there. It would be more informative to look at people who failed with the initial treatment and compare those who did and those who did not try e-cigarettes during the follow-up period. Such a comparison may well show that e-cigarette use had a positive effect. Self-selection would remain a problem, but perhaps the authors could check this?

On 2016 Nov 21, Laurie Zawertailo commented:

We thank Dr. Hajek for his constructive criticism of our paper and his suggested alternate analysis. We agree that smokers reporting e-cigarette use at follow-up may have been less likely to be able to quit using the standard treatment offered and so may have resorted to e-cigarettes to aid in their quit attempt. We were able to conduct the suggested analysis by looking at smokers who were not quit at the 3-month follow-up time point (i.e. failed on the initial treatment, n=1626). At the 6-month follow-up we assessed whether or not they reported being quit and whether or not they had used e-cigarettes. At 6-month follow-up, 11.4% of e-cigarette non-users reported quit (7-day PPA), compared to 9.2% of e-cigarette users (p=0.24, NS). Therefore, there is no evidence to support Dr. Hajek’s hypothesis that e-cigarette use will increase quit rates among those who do not quit smoking using standard evidence-based treatment (NRT plus counselling). Again these data are limited due to the lack of information regarding dose and duration of e-cigarette use and due to bias caused by self-selection.

On 2016 Nov 22, Peter Hajek commented:

Thank you Laurie for looking into this and confirming that the data do not suggest that vaping undermines quitting. Regarding a possible benefit of vaping, a better test would be including participants who were smoking at 3M, as you did, but compare those who did and those who did not try vaping BETWEEN the 3M and 6M follow-up. This is because those still smoking and reporting using EC prior to the 3M f-u are self-selected for not benefiting from vaping (up to that point anyway). Doing it the way suggested above avoids some of that problem - but the result would remain affected by self-selection and uncertainty about the purpose and intensity of e-cig use. Thanks again, Peter