- Only 51.9 per cent of youth who said they might vape went on to try it within four years.
- 28.8 per cent of youth who said they definitely wouldn’t vape tried it anyway.
- The measure did not reliably identify which young people would vape.
- Findings “question the public health relevance of susceptibility as a proxy for use” and raise questions about aggressive vape regulations.
Standard tools used to predict how likely young people are to start vaping may be overstating risk, according to a new preprint study.
The findings raise questions about the common use of “susceptibility” – a measure of whether a young person is open to trying vaping – in research and policy discussions about youth vaping.
The study analysed data from the Population Assessment of Tobacco and Health (PATH) Study, focusing on youth aged 12 to 17 who had never used vapes or cigarettes. It followed participants over a four-year period to assess whether they went on to experiment with or regularly use nicotine products.
The research was led by Dr Arielle Selya, Senior Scientist at Pinney Associates, and examined whether a ‘three-item susceptibility scale’ could reliably predict behaviour at the individual level.
Not accurate for predicting real-life behaviour
The results suggest that susceptibility does not accurately indicate which young people will go on to vape. The study found that “for a given ENDS-naïve youth who reported susceptibility to ENDS use, 51.9 per cent tried ENDS, and 15.3 per cent developed established use, within four years.” This means nearly half of those who indicated they were open to vaping never vaped at all.
At the same time, a significant number of youth who initially said they had no intention to vape later tried it anyway. According to the study, “some non-susceptible youth later tried ENDS (28.8 per cent) and cigarettes (12.5 per cent), despite initially stating intentions not to.”
Researchers described the match between susceptibility and real behaviour as weak. “The concordance between susceptibility and use was slight (Cohen’s Kappa=0.22 or lower).”
While the measure was relatively effective at ruling out who would not vape, “this came at the cost of low positive predictive value,” meaning it often failed to identify those who would.
Implications for youth vaping research and regulation
Susceptibility is a common tool used in youth tobacco research and is often treated as a stand-in for actual behaviour. It’s used in studies evaluating advertising, product risks and regulatory impacts.
The authors observe that “susceptibility is often used as a proxy for use,” under the assumption that attitudes measured through survey questions reflect future actions.
However, the findings challenge the strength of that assumption. The study “question[s] the public-health relevance of susceptibility as a proxy for use” and confirms “predictive validity of susceptibility would be limited.”
While previous studies have shown that youth who express susceptibility are more likely overall to try vaping, the lead authors note that “a statistically significant association between susceptibility and actual use does not necessarily translate into useful predictive validity.”
In other words, just because susceptibility correlates with behaviour at the group level doesn’t mean it accurately predicts individual decisions.
What the findings mean
As discussions around youth vaping and regulation continue, this research suggests that caution is needed when interpreting susceptibility data as evidence of future behaviour.
Wider debate: does vaping slow smoking declines?
The study comes amid a debate in Australia and New Zealand, where some researchers argue that vaping has “slowed the rates of decline in ever and regular-smoking” among teenagers. A series of papers led by the University of Sydney’s Professor Becky Freeman suggested that youth smoking would have fallen faster without vaping.
But other experts, including Dr Arielle Selya, question those conclusions. She notes that the claims hinge on the assumption that smoking rates would have continued to fall at the same pace in the absence of vaping, an assumption she describes as “questionable.”
Looking at the data, she said she did “not see a visually-evident change in smoking trends” in Australia and suggested that any small uptick in New Zealand is unlikely to be caused by vapes, writing: “I do find it plausible that there was a bump in smoking in New Zealand youth, but.. I don’t think it makes sense to attribute this to e-cigarettes.”
