E-cigarette companies, including giants such as British American Tobacco, have actively lobbied governments in New Zealand and Australia to weaken existing vape regulations while preventing the introduction of stricter ones.

As part of their argument, they claim that for adolescents in New Zealand, the use of e-cigarettes (vaping) might be "displacing" cigarette smoking. They argue young people are opting for vapes over traditional cigarettes.

Their key piece of evidence for this claim is an influential study published in Lancet Public Health in 2020. It concluded:

The overall decline in smoking over the past 6 years in New Zealand youth suggests that e-cigarettes might be displacing smoking.

However, in our new study published today in Lancet Regional Health-Western Pacific, we used the same data source as the 2020 study and found it does not support that conclusion.

We used a statistical approach known as logistic regression to analyse data spanning a 25-year period from 1999 to 2023, including nearly 700,000 high school students aged 14 to 15.

Before analysing the data, we knew New Zealand had made remarkable progress in reducing adolescent smoking rates in recent decades. What we wanted to know, however, is whether this progress had been affected by the emergence and rapid rise of vaping among New Zealand adolescents, beginning in about 2010.

This could potentially include vaping displacing smoking, as argued by e-cigarette companies. If this were the case, we might expect to see adolescent smoking rates decline at an even faster rate after the emergence and subsequent rise of vaping.

Alternatively, impacts might happen through a "gateway effect" where vaping increases the risks of adolescents starting to smoke. This is a theory consistently supported by findings from cohort studies, which follow individuals over time to examine how certain factors affect their health or behavioural outcomes.

Under this scenario, we might still expect to see adolescent smoking rates continuing to decline after the emergence and rise of vaping, but to decline at a slower pace than before the introduction of vapes.

From 1999 to 2023, we saw a large decline in the rates of students aged 14 or 15 "ever smoking", "smoking regularly" (daily, weekly or monthly) or smoking daily.

However, the rates of decline in "ever smoking" and "smoking regularly" slowed significantly from 2010 onwards, coinciding with the emergence of vaping in New Zealand (see figures below). The rate of decline in daily smoking did not change significantly from 2010 onwards.

In 2023, about 12.6% of 14 and 15-year-olds in New Zealand had "ever smoked" (ranging from just a few puffs to smoking daily). However, if the "ever smoking" rate had continued along its pre-2010 trajectory (before vaping emerged) this figure would have been 6.6%.

Similarly, in 2023, around 3.0% of students were "smoking regularly", but this rate would have been just 1.8% had it followed its pre-vaping trend.

Some might argue that 2010 is not the optimal year for observing changes in smoking rates related to vaping because vaping was at low levels then. However, we addressed these concerns by testing alternative "change years" from 2008 to 2018. Our findings were consistent across all years.

Others might suggest that changes in cigarette prices between 1999 and 2023 might be driving the observed slowing in the decline of smoking trends. However, even after statistically accounting for price changes, our findings remained the same.

The conclusion of the 2020 study was based solely on the observation of declining smoking rates from 2014 to 2019, a period when vaping had already become notably present among New Zealand youth.

By not assessing whether smoking trends actually changed, rather than simply declined, the study incorrectly attributed the declines between 2014 and 2019 to vaping. It did not consider whether the declines reflected a continuation, a slowing or an acceleration of pre-existing trends.

In contrast, our analysis over an extended time frame (including before the introduction of vaping in New Zealand) shows the rates of decline for both "ever smoking" and "smoking regularly" slowed significantly from 2010 onwards.

Correcting the record of the 2020 study is important because it has been used repeatedly to lobby government committees and influence policy decisions.

It was one of the most frequently cited pieces of evidence in submissions to the New Zealand parliament's health select committee, including by British American Tobacco, regarding a 2020 bill which aimed to regulate the sale and marketing of e-cigarettes.

In its submission to the Australian Parliament's select committee on tobacco harm reduction, British American Tobacco again referenced the 2020 study as important evidence to argue against the tightening of e-cigarette regulations. In its submissions to both committees, British American Tobacco quoted verbatim the flawed conclusion from the 2020 study.

Our research challenges claims that vaping might be displacing smoking among New Zealand adolescents.

Instead, our findings suggest vaping may be contributing to adolescents taking up smoking. This underlines the need for effective policies that address both vaping and smoking in New Zealand.

Other jurisdictions contemplating laws that allow easy access to vaping products for adults should carefully consider the potential for unintended consequences on young people.