On 2016 Dec 07, Zvi Herzig commented:

The authors argue that their study Gmel G, 2016 is not cross-sectional because smoking was measured at the baseline. However, both the exposure (EC use) and the outcome (cessation) are measured simultaneously at follow-up. This allows for the most basic limitation of cross-sectional studies: reverse causality.

Contrary to the authors' understanding that findings demonstrate that vaping had no beneficial effect, the negative correlation between EC and cessation likely results from successful quitters lacking the need to initiate EC use.

Their fact that EC was rare at towards the beginning of the study only exacerbates the aforementioned flaw: those quit early on had little opportunity to expose initiate e-cigarette use as smokers and hence the lower e-cigarette use among tobacco quitters.

On 2016 Jul 19, Zvi Herzig commented:

None

On 2016 Jul 19, Zvi Herzig commented:

None

On 2016 Dec 07, Zvi Herzig commented:

The authors argue that their study Gmel G, 2016 is not cross-sectional because smoking was measured at the baseline. However, both the exposure (EC use) and the outcome (cessation) are measured simultaneously at follow-up. This allows for the most basic limitation of cross-sectional studies: reverse causality.

Contrary to the authors' understanding that findings demonstrate that vaping had no beneficial effect, the negative correlation between EC and cessation likely results from successful quitters lacking the need to initiate EC use.

Their fact that EC was rare at towards the beginning of the study only exacerbates the aforementioned flaw: those quit early on had little opportunity to expose initiate e-cigarette use as smokers and hence the lower e-cigarette use among tobacco quitters.