this post was submitted on 09 Oct 2026
32 points (100.0% liked)

Explain Like I'm Five

22480 readers
41 users here now

Simplifying Complexity, One Answer at a Time!

Rules

  1. Be respectful and inclusive.
  2. No harassment, hate speech, or trolling.
  3. Engage in constructive discussions.
  4. Share relevant content.
  5. Follow guidelines and moderators' instructions.
  6. Use appropriate language and tone.
  7. Report violations.
  8. Foster a continuous learning environment.

founded 3 years ago
MODERATORS
i_stole_ur_taco@lemmy.ca
schnurrito@discuss.tchncs.de
32
ELI5: What does "a 73% average decline in wildlife populations since 1970" mean? (ourworldindata.org)
submitted 1 day ago by Artisian@lemmy.world to c/explainlikeimfive@lemmy.world
3 comments fedilink hide all child comments
 

I understand that it does not mean

this doesn’t mean 73% of populations are in decline; in fact, around half of the studied populations were in decline, while half were either increasing or stable.

Maybe I should ask why the LPI report uses such a weird number instead?

you are viewing a single comment's thread
view the rest of the comments
[–] Artisian@lemmy.world 1 points 1 day ago* (last edited 1 day ago)

My own attempt, but I'm confused.

There might be many herds of each species, all scattered in different places. The report counts all the animals in each of these herds over time, and looks at how those change. Consider some rhino's with two herds that are far apart. One of them is a giant herd, with 10000 rhinos, while the other is tiny with just 50. If the giant herd mostly dies out, and drops to 1000, while the tiny herd gets 5 times bigger to 250, then the average percent change is (-90% + 500%)/2 = +205%, even though almost all the rhinos died.

Except this is wrong; they actually take the geometric average, which I think would be sqrt( 0.1 * 5) = 0.25, a 75% decline?

Now, swap which populations do well. the 10000 rhinos become 50000 strong, and the 50 rhinos shrink to just a family or two of 10. The relative percent changes are the same; 500% for one, 10% for the other, so we would still report a 75% decline.