Let me get this off my chest please…

It’s a small thing, and once I’ve told you about it, I will move on. Probably.

I keep hearing people saying that 41% of UK species have declined in abundance since 1970. And they have (probably, at least of the species we know about)! No (major) quibbles there.

But is this bad? If the world were a stable place then over that period of time I’d expect 50% of species to have declined in abundance (some a little bit, some quite a lot) and I’d expect the other 50% to have increased (some a bit, some quite a lot). So every time I hear that figure I think ‘Not too bad then, a bit better perhaps than expected’ although I know that isn’t the message it is supposed to convey.

Now I am perfectly willing to concede that I am not entirely typical, and one area of difference is that I am a little bit more numerate than many. So I willingly concede that many people who hear the same thing think ‘41%, that’s a lot. Crikey, we must do something about that. I’ll vote Labour and send the RSPB £1000’. And that will be a good thing.

It’s a good thing, not because these people have been tricked into that thought, but because despite the fact that the fact doesn’t quite lead to the conclusion reached, if all the facts were on the table then they would.

So, as the report says, 41% of species have declined quite a lot in abundance, 33% have stayed more or less constant and 26% have increased quite a lot. So it is true that quite strong declines well outnumber quite strong increases.

I feel better for getting that off my chest.

But it leaves me wondering whether the people I hear quoting the first version realise what they are doing and are deliberately simplifying a more complex picture or whether they just have grabbed a number without thinking about it. And I’m not sure which explanation would irritate me the more.

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16 Replies to “Let me get this off my chest please…”

  1. Sadly it's the world we live in. It's all about soundbites and memes, all of which oversimplify and don't give the full picture. Plus the ever increasing pace of life, and people's correspondingly decreasing attention spans, mean that very few of us ever bother to do the reading necessary to get the full picture. We share the memes and soundbites we already agree with while disparaging those we disagree with, and no one ever changes their mind on anything anymore.

    1. The problem is that one can’t really gauge the true situation from the headline numbers.
      Many of the species that are in decline are those that migrate and which which depend on quality habitat for example wood warblers. Like wise the species that have increased are those that are able to take advantage of degraded habitats and are able to live along side humans. for example wood pigeons. So when one looks at situation this way, which I think is the right way, I think it becomes clear that things are far more serious than the headline figures portray.
      The other very important aspect is the U.K. Overseas Territories. A huge amount of species in these territories, for which the UK is entirely responsible, are facing extinction and/or are seriously endangered. Some species have already become extinct. The U.K. Overseas Territories are very often forgotten about and neglected in respect of conservation but the situation in many of these Territories is dire and needs to be addressed a.s.a.p.if we are not to loose more species.

  2. Also, mathematics is the only subject that people are proud/ pleased to admit that they don't understand.
    Whenever I meet someone who says the "don't do maths" I always ask them to lend me money,sadly it hasn't worked so far.

  3. Surely its not the headline number that matters but what the details are showing. Which species are declining and by what magnitude? What is a significant change from baseline, and if changes were drifting about at random, what should the distribution of changes be? I suspect that a statement "41% of species show a moderate or strong decline" is statistically significantly different a randomly drifted result and therefore its a reasonable thing to say, on balance.

    1. James - thank you for your first comment here. But that isn't what I hear people saying. they say '41% of UK species have declined' and that's uit as if this is a figure that should strike fear into everyone. The details matter, very much, but how they are communicated matters more in practice because a message unheard, or a message misheard, or a message mangled, is somewhere aong the continuum strtching from useful to useless to worse than useless.

  4. Perhaps you should get Tim Harford to run an item on it in 'More or Less' on Radio 4: https://www.bbc.co.uk/programmes/b006qshd
    I well remember when Ken Clarke was Education Secretary he was outraged to find that half of primary school children's reading ability was below average...

  5. What bugs me muchly is the implied accuracy in data obtained from survey. It's more honest use "about", with rounding, imho. Use of a single number to represent a complex situation is about as much use as using a single note to represent a melody.

  6. I'm intrigued by "If the world were a stable place then over that period of time I’d expect 50% of species to have declined in abundance (some a little bit, some quite a lot) and I’d expect the other 50% to have increased (some a bit, some quite a lot)." But surely species are not (necceserily) dependant on other species to decline or increase so it is quite reasonable that 100% could increase or stay the same even in a stable place (which obviously it isn't and obviously some species are dependant on each other but we are generalising here). To me there seems no reason why it should be an expected 50% decline and increase with no staying the same? Would it be possible for you to explain your expectations further please?

    1. Richard - thank you for your first comment here.

      The declines are measured since 1970. Most species vary a bit in population from year to year because of weather, food supply etc. Bird populations are pretty stable all other things being equal, but Wrens, for example, will crash in a hard winter and then bounce back over the next few years - if you measure their population change straight after a crash then it will look as though they are declining, if you measure it after many mild winters they may appear to be increasing. Insects, on the other hand, often show year to year variations in populations of many orders of magnitude. So even if the overall long term population levels were stable it would be remarkable if they were exactly the same. So, one would expect a few to have gone up and a few to have gone down (as I said). In a stable world, the ups and downs would be about the same ie as many species would have done one as the other. That's all.

      1. But why would you expect the same number to have gone up as down? Your explanation equally justifies all of them going up, all of them gonig down or all of them staying roguhly the same at the time of reporting but then you make the statement that the ups and downs would be the same and that is what I don't understand. Why would the be the same rather than any of the other options? Is it simply a statistical funtion based on the populations being treated simply as numbers rather than as actual populations that are independant of each other and could change over time in any of the ways available?

        1. Richard - it's like heads and tails on coins. You'd expect the same number of heads and tails in each year, roughly. It would be surprising if they were all heads, wouldn't it?

          1. It wouldn't surprise me if it was all heads... as that is just as likely as it being half heads and half tails... as each throw is totally independant.

  7. OK. (It is unlike you to simply dnounce someone as wrong without at least trying to explain why, I'll stop bothering you now and educate my self somewhere else.)

    1. Richard - try this then - there are many ways to get half heads and half tails but only one way to get all heads (or tails).

  8. Because I am very very very old I just haven't got a year to spin coins but my Winders 10 calculator, if my specs are not deceiving me, says if I flipped a fair coin once a day for 30 days the chance odds of all results being all one side or t'other are about one in a billion. I like to think I would smell a rat by Friday. But the odds of day 31 producing a different result are still the same. Only not with that coin.


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