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Unfortunately for all of us, the model does have very good predictive power despite its simplicity. Herrington et al in 2020 checked the 1972 model scenarios (t

Unfortunately for all of us, the model does have very good predictive power despite its simplicity. Herrington et al in 2020 checked the 1972 model scenarios (there were 4 such scenarios as sensitivity analyses) against around 40 years of empirical data and the results were close to observed ground truth [0]. 0. https://onlinelibrary.wiley.com/action/downloadSupplement?doi=10.1111%2Fjiec.13084&file=jiec13084-sup-0001-SuppMatS1.pdf https://onlinelibrary.wiley.com/action/downloadSupplement?do...

Enginerrrd 3y ago
I try not to be too harsh on here, but your interpretation of this analysis is unbelievably bad. It's absurdly easy to fit a logistic function to match the real-life logistic curve of some value of interest during the exponential phase of those functions. However... That means almost *NOTHING* with regard to the actual logistic portion which is the part people actually care about. There exist an infinite range of different logistic functions that can be made to match in the exponential portion and the majority of those functions contain almost zero information about the future logistic portion. The error between them is essentially unbounded. Calling that confirmation of predictive power is not misguided, it's just about as wrong as you can be.
- westcort 3y ago
  This is not my analysis, and the first author, Gaya Herrington, explains the alignment between the model and empirical data here: https://m.youtube.com/watch?v=KJpvc3i5j84 https://m.youtube.com/watch?v=KJpvc3i5j84 I also react with concern. Yes there are infinite curves, but there are limits to what is possible, so in actual fact there are not infinitely many possible futures here, and those futures are likely to fall within the limits of the 4 sensitivity analyses…and indeed have over more than 4 decades of follow up.
  - Enginerrrd 3y ago
    I know it's not your analysis. I said your interpretation of this analysis is flawed. You're misunderstanding that analysis to be confirmation of the predictive power of the model extrapolated into the logistic region. And you still are: >Yes there are infinite curves, but there are limits to what is possible, so in actual fact there are not infinitely many possible futures here, and those futures are likely to fall within the limits of the 4 sensitivity analyses…and indeed have over more than 4 decades of follow up. The key phrase there where your interpretation is flawed is: "are likely to fall within the limits of the 4 sensitivity analyses". That's so, so untrue. You simply cannot extrapolate logistic model parameters into the actual post-exponential-growth, logistic portion without seeing the actual logistic effects start to kick in. Those simply haven't been empirically verified here. And speaking of... the original model they are analyzing introduces limits on that exponential growth in a pretty arbitrary and artificial way, particularly when it comes to the pollution terms.... which, I'll add, this analysis shows is also the parameter they most over-estimated by a large amount even in the exponential portion.
    - westcort 3y ago
      I want to believe in infinite growth too. Maybe asteroid mining could make this paper and model predictions way off. Indeed, that is the kind of thing we hear from Jeff Bezos: https://www.milkenreview.org/articles/mining-in-space-is-coming https://www.milkenreview.org/articles/mining-in-space-is-com... But also, yes, it IS reasonable to look at 4 sensitivity analyses comprising the most common rebuttals to limits of growth, observe alignment with more than 4 decades of empirical data, and believe based on that the model is pitching well above its weight. No need for ad hominem here.
      - snapplebobapple 3y ago
        You don't have to believe in infinite growth, the problem with the model that makes the scary bit after the slopes change to down are all BS because of: "However, it is important to note that the connections in the model and the recalibration are only valid for the rising edge, as many of the variables and equations represented in the model are not physical but socio-economic. It is to be expected that the complex socio-economic relationships will be rearranged and reconnected in the event of a collapse. World3 holds the relationships between variables constant. Therefore it is not useful to draw further conclusions from the trajectory after the tipping points" That tells you this model disregards how every single societal crisis in the past was solved or at least mitigated: A massive change to the order of society (think germanic tribes conquering rome, magna carta type stuff, Napoleon et al taking France from a monarchy to an anarchy to an empire and, after calming down a bit, to a republic, etc. etc.).
ahepp 3y ago
Which of these graphs do you think supports the claim that LFG has very good predictive power? I browsed the first few, population, fertility, mortality, and food per capita. In each case the empirical data clearly diverge from all four LFG predictions, in exactly the direction I would have guessed. Or am I wrong in that analysis?

Enginerrrd 3y ago

I try not to be too harsh on here, but your interpretation of this analysis is unbelievably bad. It's absurdly easy to fit a logistic function to match the real-life logistic curve of some value of interest during the exponential phase of those functions. However... That means almost *NOTHING* with regard to the actual logistic portion which is the part people actually care about. There exist an infinite range of different logistic functions that can be made to match in the exponential portion and the majority of those functions contain almost zero information about the future logistic portion. The error between them is essentially unbounded. Calling that confirmation of predictive power is not misguided, it's just about as wrong as you can be.

westcort 3y ago
This is not my analysis, and the first author, Gaya Herrington, explains the alignment between the model and empirical data here: https://m.youtube.com/watch?v=KJpvc3i5j84 https://m.youtube.com/watch?v=KJpvc3i5j84 I also react with concern. Yes there are infinite curves, but there are limits to what is possible, so in actual fact there are not infinitely many possible futures here, and those futures are likely to fall within the limits of the 4 sensitivity analyses…and indeed have over more than 4 decades of follow up.
- Enginerrrd 3y ago
  I know it's not your analysis. I said your interpretation of this analysis is flawed. You're misunderstanding that analysis to be confirmation of the predictive power of the model extrapolated into the logistic region. And you still are: >Yes there are infinite curves, but there are limits to what is possible, so in actual fact there are not infinitely many possible futures here, and those futures are likely to fall within the limits of the 4 sensitivity analyses…and indeed have over more than 4 decades of follow up. The key phrase there where your interpretation is flawed is: "are likely to fall within the limits of the 4 sensitivity analyses". That's so, so untrue. You simply cannot extrapolate logistic model parameters into the actual post-exponential-growth, logistic portion without seeing the actual logistic effects start to kick in. Those simply haven't been empirically verified here. And speaking of... the original model they are analyzing introduces limits on that exponential growth in a pretty arbitrary and artificial way, particularly when it comes to the pollution terms.... which, I'll add, this analysis shows is also the parameter they most over-estimated by a large amount even in the exponential portion.
  - westcort 3y ago
    I want to believe in infinite growth too. Maybe asteroid mining could make this paper and model predictions way off. Indeed, that is the kind of thing we hear from Jeff Bezos: https://www.milkenreview.org/articles/mining-in-space-is-coming https://www.milkenreview.org/articles/mining-in-space-is-com... But also, yes, it IS reasonable to look at 4 sensitivity analyses comprising the most common rebuttals to limits of growth, observe alignment with more than 4 decades of empirical data, and believe based on that the model is pitching well above its weight. No need for ad hominem here.
    - snapplebobapple 3y ago
      You don't have to believe in infinite growth, the problem with the model that makes the scary bit after the slopes change to down are all BS because of: "However, it is important to note that the connections in the model and the recalibration are only valid for the rising edge, as many of the variables and equations represented in the model are not physical but socio-economic. It is to be expected that the complex socio-economic relationships will be rearranged and reconnected in the event of a collapse. World3 holds the relationships between variables constant. Therefore it is not useful to draw further conclusions from the trajectory after the tipping points" That tells you this model disregards how every single societal crisis in the past was solved or at least mitigated: A massive change to the order of society (think germanic tribes conquering rome, magna carta type stuff, Napoleon et al taking France from a monarchy to an anarchy to an empire and, after calming down a bit, to a republic, etc. etc.).

ahepp 3y ago

Which of these graphs do you think supports the claim that LFG has very good predictive power? I browsed the first few, population, fertility, mortality, and food per capita. In each case the empirical data clearly diverge from all four LFG predictions, in exactly the direction I would have guessed. Or am I wrong in that analysis?