A major new review of US vaping research is raising uncomfortable questions about how some of the most influential studies on vaping and smoking cessation are designed – and whether they may be systematically overlooking people who successfully stop smoking by switching to vapes.
The paper, published in the journal Nicotine & Tobacco Research, examined 28 studies using data from the US Population Assessment of Tobacco and Health (PATH) Study – one of the world’s largest tobacco behaviour datasets.
Digging into the papers, the researchers found something important. Studies using the same underlying dataset often reached completely different conclusions about whether vaping helps people quit smoking. Some concluded vaping promoted smoking cessation. Others found no effect. Two even suggested vaping could hinder quitting.
But when researchers looked more closely at how those studies were constructed, a pattern emerged. Studies that included smokers regardless of whether they intended to quit were far more likely to find vaping helped people stop smoking. Meanwhile, studies restricted only to smokers already planning to quit were much less likely to detect a benefit.
The findings go to the heart of a growing debate in tobacco research, which is: are some studies unintentionally, or structurally, missing the way vaping works in the real world?
The problem with looking only at “quitters”
The PATH Study is considered one of the most important tobacco research projects in the United States. Since 2013, it has followed tens of thousands of Americans over multiple survey waves, collecting detailed information about smoking, vaping and nicotine use.
Because the dataset is publicly available, many different research teams have analysed it independently. That has created a peculiar situation where researchers are often studying the same population but reaching very different conclusions.
The new review sought to understand why. Researchers identified 38 separate analyses from 28 papers using PATH data to examine whether vaping was linked to cigarette cessation. Overall, 63.2 per cent reported a positive association between vaping and quitting smoking.
But the differences became much more dramatic when researchers examined who the studies included.
Among studies using data from participants regardless of quit intention, 85 per cent reported positive findings linking vaping with smoking cessation. But among studies limited to smokers already intending to quit, only 35.3 per cent found a positive association.
The review concluded that “studies which restricted participants to those with an intention to quit were less likely to observe an association between NVP use and cessation compared to studies that included participants regardless of quit intention.”
For critics of narrow cessation models, this is a crucial distinction. Behavioural scientist Arielle Selya said the findings illustrate how seemingly technical research decisions can heavily shape conclusions.
She said: “This review article showed that a key issue in studies on whether e-cigarettes lead to stopping smoking is whether or not you include people who were using e-cigarettes with the specific preplanned intention to quit.
“Only about 15 per cent of adults who smoke are planning to quit in the next month, and only a fraction of those will use e-cigarettes in their quit attempt. But if you include everyone who used e-cigarettes – regardless of the reason – the evidence is a lot stronger that e-cigarettes can help people stop smoking, including via ‘accidental switching.’”
The “accidental quitter” problem
The idea of “accidental quitting” appears central to the debate. Traditional smoking cessation research often treats quitting as a planned medical event: a smoker decides to stop, uses a cessation aid and attempts abstinence.
But vaping may not always fit neatly into that model. Some smokers begin vaping for reasons unrelated to formally quitting – curiosity, convenience, cost, social reasons, flavour preferences or reduced smoke smell – and gradually reduce or abandon cigarettes over time.
According to harm reduction advocates, those smokers can disappear from analyses if researchers only study people who explicitly report an intention to quit smoking.
Clive Bates said this distinction is fundamental. “There is little doubt that vaping has been displacing smoking in the American population, with the greatest success at younger ages,” he said.
“However, it is possible to hide this effect by manipulating surveys such as PATH. If you only look at people who say they are trying to quit, you will miss a huge number of people who just want to use nicotine differently and drift into giving up smoking because they prefer vaping.
“These people become what we sometimes call accidental quitters. These are often the most important switchers, as they would likely have continued to smoke indefinitely.”
Bates argued that treating vaping purely as a cessation therapy misunderstands how many consumers actually use it.
He said: “Vaping is not primarily a smoking cessation aid; it is a different and lower-risk way of using nicotine. So if researchers treat it like a smoking cessation aid, they will produce distorted results.”
Missing the switchers between survey waves
Another issue highlighted by both the review and outside experts involves timing.
The PATH Study collects data in waves, typically separated by long intervals. That creates a challenge when nicotine behaviour changes rapidly.
A smoker may switch to vaping, stop smoking entirely and later stop vaping too – all between survey waves. If researchers only observe the person at the beginning and end of that period, the switch itself may never appear in the data.
The review acknowledged that study design choices around timing, exposure definitions and outcome measurements varied widely across analyses.
Selya said this can create an important blind spot.
“The decisions about study design and analysis can sometimes have huge influence over what the results show and what conclusions are drawn,” she said.
“In this case it’s about who is included in the analysis, but there are other issues too. For example, the way people typically analyse PATH often fails to capture people who successfully switched quickly and in between PATH surveys, and as a result it oversamples people who smoke cigarettes or dual use for longer periods.”
Bates raised a similar concern. “Vaping has also been successful as an aid to complete smoking cessation, like a kind of souped-up nicotine replacement therapy,” he said.
“However, there are several ways to accidentally miss or deliberately conceal this effect. For example, if vaping is used for a short period of time between successive waves of the PATH survey, it may look as if a person who has gone from smoking to complete abstinence and has never touched a vape.”
This issue may be especially important when studying smokers who use vapes temporarily as transitional tools rather than long-term substitutes.
The dual use debate
One of the most contested issues in vaping research is so-called “dual use” – when people both smoke cigarettes and vape. Critics sometimes interpret dual use as evidence that vaping prevents smokers from quitting completely.
But the review suggests the reality may be more complicated. The authors noted that many studies differed substantially in how they defined vaping exposure, smoking outcomes and patterns of use. Some examined daily vaping, others occasional use, others multi-wave behavioural patterns.
Importantly, the review found daily vaping appeared much more strongly associated with quitting than occasional use.
Among 19 studies that included a daily vaping category, 17 reported a positive association between vaping and smoking cessation. The paper concluded that “daily NVP use may support smoking cessation.”
Bates argued that persistent dual use may sometimes reflect heavier nicotine dependence rather than failure.
He said: “People who are engaged in so-called dual use may appear as though vaping is preventing them from quitting completely, though it usually just means they are more dependent on smoking and, without vapes, would just carry on smoking as usual.”
That distinction matters because observational studies can struggle to separate cause from correlation.
Heavier smokers may be more likely both to vape and to struggle quitting, making vaping appear ineffective even if it is helping reduce cigarette consumption.
The review repeatedly emphasised that observational research is vulnerable to these types of confounding problems.
One dataset, many conclusions
Perhaps the most revealing aspect of the review is not simply that studies disagreed, but how dramatically research choices appeared to shape findings.
The paper describes these decisions as “researcher degrees of freedom.”
Different teams selected different populations, different definitions of vaping, different cessation outcomes, different covariates and different statistical methods.
The result was that studies using the same underlying data often produced conflicting headlines. The authors warned against relying on any single PATH analysis to make sweeping claims about vaping and smoking cessation.
“Researchers are advised against making broad claims based on any single PATH Study analysis of NVP use and smoking cessation,” the paper stated.
Instead, the authors argued researchers must examine patterns across multiple studies and understand what methodological choices may be driving differences.
The paper also called for greater transparency, clearer reporting standards and more open analytical practices.
What it means for vape policy
The debate extends far beyond academia. Observational studies using PATH data have played a major role in shaping public discussions around vaping regulation, smoking cessation policy and perceptions of risk.
Some analyses suggesting vaping does not help smokers quit have been widely cited in arguments for tighter restrictions on vape products.
But if certain study designs are systematically missing successful switchers, critics argue policymakers may be getting an incomplete picture of how vaping operates in real-world populations.
The review does not claim vaping definitively helps all smokers quit, nor does it dismiss the challenges of studying long-term nicotine behaviour. In fact, the authors repeatedly stress the limitations of observational research and the need for better methods.
But the paper raises an important possibility: some smokers who successfully leave cigarettes behind may effectively vanish from commonly used research frameworks.
And if that is happening, it could help explain why public health debates around vaping often appear so contradictory, even when researchers are analysing the same data.
Arielle Selya is an employee of Pinney Associates, which consults to Juul Labs on tobacco harm reduction. She also serves as a scientific advisor to the Global Forum on Nicotine. Her opinions here are her own and do not necessarily reflect those of her clients or employers.
