media

Zombie stats and hair-trigger outrage: reflections of a Twitter addict

It seems somehow odd to come over all reflective about Twitter, that most impulsive of online communication channels. But over the year or so that I’ve been using it as a kind of super-effective personalised newsfeed, several cautionary tales have played out in my Twitter feed, which I have here distilled into two key lessons. First: distrust numbers, even – especially – those whose implications sit well with your worldview. And second, reign in your outrage: issues are almost certainly more complicated than 140 characters allow. Twitter, by its very nature, gives you soundbites. If you’re lucky, you’ll get a link to something more substantial, but it is so very easy to retweet something that appeals to your sense of how the world works without scrutinising the numbers. My favourite example (not least because it got me onto BBC R4’s More or Less!) is the ludicrous ‘100 Cod in the North Sea’ story that I blogged about last year. Now it takes just a moment’s thought, if that, to realise that this number is very very wrong (by a factor of at least several hundreds of thousands, in fact). But it played so nicely into the ‘overfishing is devastating our seas’ narrative that many people declined to give it that moment, and unthinkingly retweeted.

This is just one example, but my Twitter feed is full of them. I’m interested in the natural environment, and the impacts that we are having upon it, so I follow a range of environmental groups who tend, for instance, to jump immediately on numbers making renewable energy look especially attractive. Now climate change terrifies me, and I am fully behind the idea that we need to decarbonise the economy as a matter of some urgency. But I also agree wholeheartedly with David McKay who, discussing the favourable carbon footprint on nuclear power in his (essential, free) Without the Hot Air, states “I’m not trying to be pro-nuclear. I’m just pro-arithmetic”. Fortunately, the vigilance of people such as Robert Wilson (@CarbonCounter_) provides a corrective to some of these numbers (see for example his dissection of an awfully inaccurate Guardian report on costs to consumers of gas vs. renewables). But such arguments rarely translate so well to Twitter soundbites and so the zombie stats – numbers that we know are wrong, but which are appealing – refuse to die.

What’s the harm in all this? In my post on the cod story I mentioned the fragile trust that now exists between the fishing, scientific and conservation communities which has led to promising progress in the recovery of North Sea cod stocks but which can easily be shattered by the promulgation of laughable statistics. More generally, dubious numbers muddy whatever water they fall into. In his excellent critique of mainstream economics The Skeptical Economist, which I reviewed previously, Jonathan Aldred warns that “dubious numbers are infectious: adding a dubious number to a reliable one yields an equally dubious number”. Which leads me to propose Mola mola’s second law1:

An argument advances with the rigour of its most dubious number

So it doesn’t matter how watertight the ethical case for regulating cod fisheries, or for moving away from fossil fuels; if you use farcical numbers to advance this case, the argument will fail to progress.

Another consequence of these kinds of zombie stats is the hair-trigger outrage for which Twitter is (in)famous. This applies just as much to the niche worlds of the practice and administration of science as it does to Westminster or celebrity gossip. In particular, it is rare for a day to pass without some call appearing in my timeline to sign a superficially worthy-looking petition. I am extremely wary of doing so, for a couple of reasons.

For instance, a while back I signed something against some kind of reforms (I didn’t read the details) in a European marine institute which I have visited a few times and where I have friends and colleagues. Surely I should support them in their hour of need? Hmmm. Well. Next time I went, my friend – an extremely conscientious and committed member of the institute – said words to the effect of ‘Please, nobody sign that petition. These reforms are exactly what we need and the people fighting against them do nothing here.’ Duly chastised, I resolved to be more discerning in future.

Then there was the curious incident of Nerc’s planned merger of the British Antarctic Survey with the National Oceanography Centre. Now it is my view that Nerc handled this pretty poorly, but although there were some pretty convincing arguments – both scientific and geopolitical – against this merger, there were good arguments for it too, and chatting to people I know at both NOC and BAS (as well as reading things like this excellent coverage from Mark Brandon) just confirmed to me that this was very far from the black and white issue painted by many environmental journalists and pressure groups who backed a petition against it. And the joy which met the announcement that the merger (which is what was proposed, although it was typically presented as the 'dismantling' or ‘abolition’ of BAS) made no mention of the budgetary constraints at Nerc which had prompted the proposal, which still exist, and which will now require that savings be made in some other area of environmental science.

To reiterate: I don’t know whether the correct decision was made. But that’s precisely the point. I know the issues and institutions involved pretty well, yet didn’t feel sufficiently well-informed to decide one way or another. In such a case, it would be hugely irresponsible of me to sign any petition. Yet many thousands of people did. Call me an old cynic, but I doubt all that many of them had read widely on the rationale for the merger. Sadly, it is now far easier to create a petition – let alone sign one – than it is to inform yourself about an issue. Of course, the UK government has made a rod for its own back here with e-petitions initiative and its commitment to debate in parliament any issue that gains 100,000 signatures. But it is our responsibility as thoughtful citizens to take the issue of signing a petition seriously. Which usually means basing our opinions on more than 140 characters of research.

Bearing these caveats in mind, and keeping critical faculties engaged at (almost) all times, Twitter remains for me an essential source of information, conversation and debate, and an invaluable means to publicise work and opportunities, and I encourage non-tweeters to have a go - good guides for sciencey-minded beginners here, here, here and here.

1First law here

Putting facts in the way of a good story

Or: 100 cod in the North Sea? I’ve just had a nice weekend almost completely away from screens of all kinds, and was starting to think ‘perhaps it’s time to curtail some of my online activity <cough> Twitter <cough>’. But a quick scan down my timeline on a Monday morning couldn’t hurt could it?

Best laid plans and all that… One of the first things I saw was this, from @rivercottage: Just 100 cod left in North Sea. Now I’m a big fan of Hugh F-W, I own (too?) many of his cookbooks, have eaten in his canteen, and admire his campaigning work. BUT: Just 100 cod left in North Sea? Shurly shome mishtake?

I kept scanning, and the same figure kept appearing: 100 cod in the North Sea. All of these tweets linked to a Daily Telegraph story which I duly looked up when I got to work and there it was, under the headline “Just 100 cod left in North Sea” and the only marginally less ludicrous subheading “Overfishing has left fewer than 100 adult cod in the North Sea, it was reported”: a summary of a recent Cefas survey of catches at European ports. (To be fair to the Telegraph, an almost identical piece appeared in (hold your nose) the Mail, although the headline there made the made the ‘100 adult cod’ claim more clear.) Now I know people at Cefas, I trust them to do good surveys (although there’s no link to the actual report in either the Telegraph or the Mail piece, and I can't find it on the Cefas website), so could this 100 cod figure possibly be true?

Short answer: No. Of course it couldn’t.

What the survey found was that last year, “fishermen did not catch a single cod over the age of 13”, and Chris Darby of Cefas is quoted as saying that this suggests “there are fewer than 100 such fish in the whole North Sea”. This rather uncontroversial statement from Darby is the source of the headline and thus, the Twitter meme. Anyone reading the article, though, will see that the survey did find 191 million 1 year old cod, 18 million 3 year olds, and 65,300 tons of cod aged 3 or more years. So "Just 100 cod left in North Sea" is, as @BobOHara put it, an impressively wrong headline.

But what about the subheading about adult cod? Do cod mature as late as 13? No. From Fishbase figures, North Sea cod mature at 3-4 years. So a good proportion of those 18 million 3 year olds, and most of the 65,300 tons of 3+ y fish, will be adults. Subheading debunked too then.

As for the wider issue of overfishing and the state of the cod stock in the North sea, there is some information in the article, namely that the 65,300 tons of 3+ fish is a reduction from the 276,000 in 1971, “a peak year for cod population”, although no indication of whether the 2011 figure is any kind of historic low. But the number of 13+ year old fish is presented in glorious isolation: although no fish of that age were caught in 2011, I have no idea from this article when last such a fish was caught. I suspect some time ago, for a couple of reasons.

First, although the article quotes a maximum age for cod of 25y, which is indeed the figure given in Fishbase (taken, if you follow through to the references, from a 1974 Collins Guide to the Sea Fishes of Britain and North Western Europe book), looking at stock-specific data, again from Fishbase, gives one figure for North Sea cod: 11y (and this from a study published in 1959).

Second, an anecdote: way back before I started my PhD I worked for a while at Cefas. I shared an office with a guy who was interested in the age structure of cod stocks, and who used the annual growth rings on cod otoliths (inner ear bones) to get a handle on this. While I was there, someone sent in an otolith with 7 annual growth rings taken from a cod caught in the Irish Sea (as I recall; so a different stock, but still…). He was over the moon, because cod as old as 7 were so scarce in his dataset. That was 15 years ago.

Even if we accept that 13 is an attainable age for North Sea cod, then, it’s certainly a ripe old age, so saying from these data that there are 100 adult cod left in the North Sea is like saying there are 12,640 adults living in the UK based on the number of centurions.

I don’t want to downplay the perilous state of many fish stocks, nor the fact that overfishing is primarily what’s led them there. Another statistic in the Telegraph piece is sobering: the Cefas team estimated a 2011 population of 600 cod aged 12-13, of which 200 were caught. This tallies with another personal anecdote, this time from my undergraduate project working on data obtained from tagging North Sea plaice. These tags were returned to Cefas by fishermen when they caught a tagged plaice. We reckoned on a 30% return rate within a year. So: chuck a commercially important adult fish into the North Sea, and it has about a 1/3 chance of being caught within a year. That’s pretty intensive fishing. Likewise, there’s a load of good work – much of it by Cefas scientists – showing for instance how the biomass of big fish in the North Sea is massively reduced compared to predictions of the situation with no fishing.

Given this background, isn’t it perhaps a good thing to highlight fisheries in crisis? A few people I interacted with on Twitter over this seemed to think so, for example @oceanCO2 said title is certainly misleading but the article itself has context for the numbers. As you say ‘100 cod left’ does catch the eye! and @S_Danielsson wrote situation bad even if tweets are a bit oversimplified, 93% of NS cod are caught before reproductive age. Here and elsewhere both have made reasonable points, but I cannot agree that using misleading numbers to make a point is ever justified. In this specific case, just look at the responses of some in the fishing industry, for instance @LapwingPD972 who’s been fishing the North Sea for 33 years: Who are these people that say there is only 100 mature Cod left in the north sea,OMG invitation to anyone,come away on my boat to see fish to which @AjaxAH32 (skipper with 30y experience) replied I thought it was 1st of April Brian.

This matters because the relationship between fishers, scientists and conservationists in the UK is often fraught; but listening to various talks at the Oceans of Potential meeting in Plymouth last week I really felt that real progress has been made, with a focus on the business case for sustainability which everyone can buy into. Silly headlines – seemingly designed to be picked up and circulated without thought around Twitter – set back these efforts and risk returning us to a harmful new cod war of words. More generally, you really don’t strengthen your case by simply parroting obviously nonsensical numbers.

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Postscript (19/09/12)

Since I wrote the above, Defra have released an official myth bust statement, worth quoting in full here:

The myth: An article in The Sunday Times claimed that ‘fewer than 100 mature cod are left in the North Sea’.

The truth: This is completely wrong, in fact we know there to be around 21 million mature cod in the north sea. Cod start to mature from six months old and are fully mature at age six.  There are a small number of cod over the age of 12 years old which has always been the case in the North Sea even when fished at lower levels in the 1950s and 1960s. Cod older than 15 have never been recorded in the North Sea.

So - the Sunday Times, Telegraph and Mail were out by a cool factor of 210,000…