reuters.com
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Nearly 6,000 monitored vertebrate species across more than 35,000 populations declined by an average of 73% from 1970 to 2022, the World Wide Fund ​for Nature said in its latest Living Planet Report published on Thursday.

  • Artisian@lemmy.worldEnglish
    6·
    21 hours ago

    This is a famously difficult to interpret statistic. It’s an excellent survey, but you probably do not understand what the number means (because it is a weird number). In particular, only half of species surveyed showed a population decline at all, the other half either grew or were stagnant.

    The authors of the LPI go to great lengths to explain this. Yet, there is inevitably a long list of headlines claiming that we’ve “lost 73% of wildlife”, “73% of species have gone extinct”, or “73% of species are declining”. All of these are incorrect.

    To give you another sense that this number is weird:

    The 2022 Living Planet Index reported an average decline of 69% since 1970. In 2024, it reported a 73% decline. And this latest report finds the same: 73%.

    So, what exactly is this 73% number?

    To obtain the final LPI number, researchers take the geometric mean of the rates of change across all these populations. They also provide different weights to different populations, which affects the final result.

    I don’t know other places where I’d take the geometric mean. I have no intuition for it. So… caution advised.

    • Artisian@lemmy.worldEnglish
      1·
      20 hours ago

      Ok; I’ve thought through several examples. The geometric mean is heavily biased to show a decrease IMO. A species could have it’s total population grow substantially, but if most of that growth is to already large/successful subsets, then it’ll almost certainly show as a negative (geometric) average change, even with ~noise on the other populations. I think you should only see a positive metric here if most species measured are invasive; growing extremely fast in places not prepared for them. (and being careful not to measure the things getting killed by the new invaders)