Monthly Archives: March 2015

Dodgy reporting, Public health

Vaping among teenagers

4 Comments

Vaping, or use of e-cigarettes, has the potential to be a huge advance in public health. It provides an alternative to smoking that allows addicted smokers to get their nicotine fix without exposing them to all the harmful chemicals in cigarette smoke. This is a development that should be welcomed with open arms by everyone in the public health community, though oddly, it doesn’t seem to be. Many in the public health community are very much against vaping. The reasons for that might make an interesting blogpost for another day.

But today, I want to talk about a piece of research into vaping among teenagers that’s been in the news a lot today.

Despite the obvious upside of vaping, there are potential downsides. The concern is that it may be seen as a “gateway” to smoking. There is a theoretical risk that teenagers may be attracted to vaping and subsequently take up smoking. Obviously that would be a thoroughly bad thing for public health.

Clearly, it is an area that is important to research so that we can better understand what the downside might be of vaping.

So I was interested to see that a study has been published today that looks specifically at smoking among teenagers. Can that help to shed light on these important questions?

Looking at some of the stories in the popular media, you might think it could. We are told that e-cigs are the “alcopops of the nicotine world“, that there are “high rates of usage among secondary school pupils” and that e-cigs are “encouraging people to take up smoking“.

Those claims are, to use a technical term, bollocks.

Let’s look at what the researchers actually did. They used cross sectional questionnaire data in which a single question was asked about vaping: “have you ever tried or purchased e-cigarettes?”

The first thing to note is that the statistics are about the number of teenagers who have ever tried vaping. So they will be included in the statistics if they tried it once. Perhaps they were at a party and they had a single puff on a mate’s e-cig. The study gives us absolutely no information on the proportion of teenagers who vaped regularly. So to conclude “high rates of usage” just isn’t backed up by any evidence. Overall, about 1 in 5 of the teenagers answered yes to the question. Without knowing how many of those became regular users, it becomes very hard to draw any conclusions from the study.

But it gets worse.

The claim that vaping is encouraging people to take up smoking isn’t even remotely supported by the data. To do that, you would need to know what proportion of teenagers who hadn’t previously smoked try vaping, and subsequently go on to start smoking. Given that the present study is a cross sectional one (ie participants were studied only at a single point in time), it provides absolutely no information on that.

Even if you did know that, it wouldn’t tell you that vaping was necessarily a gateway to smoking. Maybe teenagers who start vaping and subsequently start smoking would have smoked anyway. To untangle that, you’d ideally need a randomised trial of areas in which vaping is available and areas in which it isn’t, though I can’t see that ever being done. The next best thing would be to look at changes in the prevalence of smoking among teenagers before and after vaping became available. If it increased after vaping became available, that might give you some reason to think vaping is acting as a gateway to smoking. But the current study provides absolutely no information to help with this question.

I’ve filed post this under “Dodgy reporting”, and of course the journalists who wrote about the study in such uncritical terms really should have known better, but actually I think the real fault lies here with the authors of the paper. In their conclusions, they write “Findings suggest that e-cigarettes are being accessed by teenagers more for experimentation than smoking cessation.”

No, they really don’t show that at all. Of those teenagers who had tried e-cigs, only 15.8% were never-smokers. And bear in mind that most of the overall sample (61.2%) were never-smokers. That suggests that e-cigs are far more likely to be used by current or former smokers than by non-smokers. In fact while only 4.9% of never smokers had tried e-cigs, (remember, that may mean only trying them once), 50.7% of ex-smokers had tried them. So a more reasonable conclusion might be that vaping is helping ex-smokers to quit, though in fact I don’t think it’s possible even to conclude that much from a cross-sectional study that didn’t measure whether vaping was a one-off puff or a habit.

While there are some important questions to be asked about how vaping is used by teenagers, I’m afraid this new study does absolutely nothing to help answer them.

 Update 1 April:

It seems I’m not the only person in the blogosphere to pick up some of the problems with the way this study has been spun. Here’s a good blogpost from Clive Bates, which as well as making several important points in its own right also contains links to some other interesting comment on the study.

 

Dodgy statistics

Tobacco vs teddy bears

Leave a comment

Now, before we go any further, I’d like to make one thing really clear. Smoking is bad for you. It’s really bad for you. Anything that results in fewer people smoking is likely to be a thoroughly good thing for public health.

But sadly, I have to say there are times when I think the anti-tobacco movement is losing the plot. One such time came this week when I saw the headline “Industry makes $7,000 for each tobacco death“. That has to be one of the daftest statistics I’ve seen for a long time, and I speak as someone who takes a keen interest in daft statistics.

I’m not saying the number is wrong. I haven’t checked it in detail, so it could be, but that’s not the point, and in any case, the numbers look more or less plausible.

The calculation goes like this. Total tobacco industry profits in 2013 (the most recent year for which figures are available) were $44 billion. In the same year, 6.3 million people died from smoking related diseases. Divide the first number by the second, and you end up with $7000 profit per death.

I think we’re supposed to be shocked by that. Perhaps the message is that the tobacco industry is profiting from deaths. In fact given we are told that this figure has increased from $6000 a couple of years ago as if that were a bad thing, I guess that is what we’re supposed to think.

If you haven’t yet figured out how absurd that is, let’s compare it with the teddy bear industry.

Now, some of the figures that follow come from sources that might not score 10/10 for reliability, and these calculations might look like they’ve been made up on the back of a fag packet.  But please bear with me, because all that we really require for today’s purposes is that these numbers be at least approximately correct to within a couple of orders of magnitude, and I think they probably are.

Let’s start with the number of teddy bear related deaths each year. I haven’t been able to find reliable global figures for that, but according to this website, there are 22 fatal incidents involving teddy bears and other toys in the US each year. Let’s assume that teddy bears account for half of those. That gives us 11 teddy bear related deaths per year in the US.

Since we’re looking at the US, how much profit does the US teddy bear industry make each year? I’ve struggled to find good figures for that, but I think we can get a rough idea by looking at the profits of the Vermont Teddy Bear Company, which is apparently one of the largest players in the US teddy bear market. I don’t know what their market share is. Let’s just take a wild guess that it’s about 1/3 of the total teddy bear market.

The company is now owned by private equity and so isn’t required to report its profits, but I found some figures from the last few years (2001 to 2005) before it was bought by private equity, and its average annual profit for that period was about $1.7 million. So if that represents 1/3 of the total teddy bear market, and if its competitors are similarly profitable (wild assumptions I know, but we’re only going for wild approximations here), then the total annual profits of the US teddy bear market are about £5 million.

So, if we now do the same calculation as for the tobacco industry, we see that the teddy bear industry makes a profit of about $450,000 per death ($5 million divided by 11 deaths).

So do we conclude that the teddy bear industry is far more evil than the tobacco industry?

No. What we conclude is that using “profits per death” as a measure of the social harm of an industry is an incredibly daft use of statistics. You are dividing by the number of deaths, so the more people you kill, the smaller will be your profits per death.

There are many statistics you could choose to show the harms of the tobacco industry. That it kills about half its users is a good place to start.  That chronic obstructive pulmonary disease, a disease that is massively associated with smoking, is the world’s third leading cause of death, also makes a pretty powerful point. Or one of my personal favourite statistics about smoking, that a 35-year-old smoker is twice as likely to die before age 70 as a non-smoker of the same age.

But let’s not try to show how bad smoking is by using a measure which increases the fewer people your product kills, OK?