Category Archives: Dodgy statistics

Conflicts of interest, Dodgy reporting, Dodgy statistics, Public health

Are strokes really rising in young people?

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I woke up to the news this morning that there has been an alarming increase in the number of strokes in people aged 40-54.

My first thought was “this has been sponsored by a stroke charity, so they probably have an interest in making the figures seem alarming”. So I wondered how robust the research was that led to this conclusion.

The article above did not link to a published paper describing the research. So I looked on the Stroke Association’s website. There, I found a press release. This press release also didn’t link to any published paper, which makes me think that there is no published paper. It’s hard to believe a press release describing a new piece of research would fail to tell you if it had been published in a respectable journal.

The press release describes data on hospital admissions provided by the NHS, which shows that the number of men aged 40 to 54 admitted to hospital with strokes increased from 4260 in the year 2000 to to 6221 in 2014, and the equivalent figures for women were an increase from 3529 to 4604.

Well, yes, those figures are certainly substantial increases. But there could be various different reasons for them, some worrying, others reassuring.

It is possible, as the press release certainly wants us to believe, that the main reason for the increase is that strokes are becoming more common. However, it is also possible that recognition of stroke has improved, or that stroke patients are more likely now to get the hospital treatment they need than in the past. Both of those latter explanations would be good things.

So how do the stroke association distinguish among those possibilities?

Well, they don’t. The press release says “It is thought that the rise is due to increasing sedentary and unhealthy lifestyles, and changes in hospital admission practice.”

“It is thought that”? Seriously? Who thinks that? And why do they think it?

It’s nice that the Stroke Association acknowledge the possibility that part of the reason might be changes in hospital admission practice, but given that the title of the press release is “Stroke rates soar among men and women in their 40s and 50s” (note: not “Rates of hospital admission due to stroke soar”), there can be no doubt which message the Stroke Association want to emphasise.

I’m sorry, but they’re going to need better evidence than “it is thought that” to convince me they have teased out the relative contributions of different factors to the rise in hospital admissions.

Dodgy statistics

Tobacco vs teddy bears

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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?