95% Less Harmful – the Story of a Statistic

When Public Health England (PHE) published their recent report on e cigarettes, the statistic to hit the headlines was the claim that the electronic variety were ‘95% less harmful’ than standard cigarettes. It’s a figure that will have entered the collective consciousness of journalists and vaping enthusiasts, and I can guarantee that we will hear it quoted again and again in coming months and years.

The question is: where has it come from, and what does it mean?

The first question is easy to answer: the 95% figure does not come from PHE. Their report simply quotes the estimates made by another group of experts published by Nutt et al in European Addiction Research. Simply put, PHE have said: ‘other experts have guessed that e cigarettes are 95% less harmful than standard cigarettes, and that seems about right to us.’

The over reliance on the findings of another group of experts has received some very public criticism – most notably in an editorial in The Lancet when it emerged that the findings of this group had been funded by an organisation with links to industry, and that three of its authors had significant financial conflicts of interest. These are valid points, although they may have been made better if The Lancet had included the author’s name and declaration of interests alongside the editorial.

The second question is harder to answer, and here is my main concern with how the 95% figure has been presented. What does ‘95% less harmful’ actually mean?

If I were a smoker, wondering whether to switch to vaping, I would primarily be interested in one thing: how harmful are they to me. In other words – am I less likely to die or get ill if I switch to e cigarettes?

Well, the PHE report would seem to answer this question – in the forward to the full report the authors state that e cigarettes are ‘95% less harmful to your health than smoking.’ The trouble is that the report where they obtained the 95% figure looked at far more than just the effects of smoking on the health of an individual.

The piece of work by Nutt and colleagues involved a group of experts being asked to estimate the harm of a range of nicotine products against 12 different criteria – these included the risk to individual health, but also other societal harms such as economic impact, international damage and links with crime. The 95% figure was only achieved after all 12 factors were weighted for importance and then each nicotine containing product was given a composite score.

Now the propensity for a commercial product to be linked with criminal activity may be very important to PHE, but it wouldn’t influence my individual health choice, nor the advice I would want to give to patients.

Moreover, the work by Nutt and colleagues includes this statement: ‘Perhaps not surprisingly, given their massively greater use as compared with other products, cigarettes were ranked the most harmful.’ So the research was greatly influenced by the extent to which products are used. On this basis you could conclude that drinking wine is more harmful than drinking methylated spirits – on a population basis this is true, but it would be a poor basis for individual advice. 

In response to the criticism in The Lancet, PHE produced a subsequent statement in order to try to achieve some clarity over the 95% figure – only to muddy the waters further by claiming that the figure was linked to the fact that there are 95% fewer harmful chemicals in e cigarettes than standard cigarettes. This may well be true – but it is not the reason why they gave the 95% figure in the first place. It also assumes a linear relationship between the amount of chemical and the degree of harm – 5% of the chemical might only cause 1% of the harm, or it could be 50%.

One of the main problems I have with the 95% statistic, therefore, is one of principle – I just don’t like being duped by the misuse of statistics.

My second issue, however, is more pragmatic: the statistic does not help us with some of the key questions we need to answer.

That e cigarettes are safer than standard cigarettes is not much in doubt – mostly on the basis that smoking is so bad for health that it isn’t hard to beat. There is clearly much to be gained by smokers switching to the electronic variety. The next question concerns what smokers should do next.

Much is said about e cigarettes being an aid to quitting, but what is unique about them is that people often stay with them for the longterm, in a way that they would never consider with something like a nicotine patch. This may be their greatest strength – people may be able to quit who could never do so before – but it is also a new phenomenon as longterm nicotine substitution becomes the norm.

Are e cigarettes so safe that once smokers move over to them they can consider the job done? Many vapers talk about it in these terms. For the short term, it seems they are safe. They have been in common use for 5-8 years and there have been no major concerns so far (although acute poisoning is a new problem with liquid nicotine) – but then the same is true for cigarettes where it is use over decades that is the problem. For me, the 95% figure is too questionable to be able to help here.

There are more dilemmas I face as a doctor since I need to know how to interpret the health risks of someone who uses an electronic cigarette. When it comes to cardiovascular risk, should I consider them a smoker, a non-smoker, or something in between? If they have a persistent cough, do I suggest a chest x-ray early on the grounds that they are at increased risk, or can we watch and wait for a while?

We are a long way from being able to answer questions like this, and I would have preferred a little more honesty from PHE about what we don’t yet know, a little less reliance on the opinions of experts, and only to be presented with a figure like 95% if it is based on hard, objective evidence.