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> Time series forecasting […] is hard […] > Leaving modeling up to the professionals is completely the wrong lesson. I don’t understand what you’re saying. No

by FabHK 7y ago

> Time series forecasting […] is hard […] > Leaving modeling up to the professionals is completely the wrong lesson. I don’t understand what you’re saying. Nobody is advocating that amateurs be precluded from modeling to their heart’s content. So what are you advocating? One should discard models from professionals? One should prefer models from non-experts? One should crowdsource models? One should make policy decisions based on gut instinct?

ignoramous 7y ago
> I don’t understand what you’re saying. I think what GP means is, leaving it upto professionals alone is a recipe for disaster because of the inherent corruption, greed, biases, and prejudices at play. > So what are you advocating? Not speaking for GP, but simpler models are more likely to be a good approximation and more than enough, anyway [0]? Simplicity helps because it stops the pundits and politicians from sort of running away with it? [0] Newton's theory of gravitation has been supplanted by Einstein's theory of relativity and yet Newton's theory remains generally "empirically adequate". Indeed, Newton's theory generally has excellent predictive power. Yet Newton's theory is not an approximation of Einstein's theory. For illustration, consider an apple falling down from a tree. Under Newton's theory, the apple falls because Earth exerts a force on the apple—what is called "the force of gravity". Under Einstein's theory, Earth does not exert any force on the apple. Hence, Newton's theory might be regarded as being, in some sense, completely wrong but extremely useful (The usefulness of Newton's theory comes partly from being vastly simpler, both mathematically and computationally, than Einstein's theory). https://en.wikipedia.org/wiki/All_models_are_wrong https://en.wikipedia.org/wiki/All_models_are_wrong
- FabHK 7y ago
  > because of the inherent corruption, greed, biases, and prejudices at play. You and I must be thinking of different professionals. At any rate, here are two very very very simple models of this epidemic: a) cases will grow linearly, b) cases will grow exponentially. Super simple. extremely different outcome. Now, one still has to make policy decisions. I think the solution is not fewer professionals, but more and better professionals.
  - samatman 7y ago
    Both of these are wrong, and the exponential one becomes more wrong faster, while being a better match for the beginning of the curve. Exponential processes don't exist in nature, they always break into some other curve at some point.
    - jhayward 7y ago
      This is a useless bit of pedantry. The exponential portion of the sigmoid curve is the only part that matters to human health, survival, and economic well-being.
      - samatman 7y ago
        Then why, pray tell, is the title of the article we are discussing not "Forecasting exponential curves is hard"? The entire point is that forecasting exponentials is easy but becomes badly wrong at some point and that point is difficult to forecast
      - nl 7y ago
        No it's absolutely not!! Epidemics are (more) properly modelled by the Gompertz function[1], and the position of the "transition" between the exponential portion and non-exponential points it the important point. That is exactly what the person you are replying to is saying ("they always break into some other curve at some point."). [1] https://en.wikipedia.org/wiki/Gompertz_function https://en.wikipedia.org/wiki/Gompertz_function
        BaronSamedi 7y ago
        Is the Gompertz function the function behind the standard "epi curve"? It appears from the CDC web site and other places that the epi curve is the standard way epidemics are modeled. The CDC even has a simple tutorial for creating them: https://www.cdc.gov/training/quicklearns/createepi/index.html https://www.cdc.gov/training/quicklearns/createepi/index.htm...
- haneefmubarak 7y ago
  If Einstein's theory roughly says that massive objects deform space proportional to their mass, the effect of which is that massive objects (all else held equal) will tend to move towards each other more so than they would otherwise; meanwhile Newton's theory says that massive objects attract each other proportional to the product of their masses divided by the square of their distance; and Newton's theory does in the vast majority of useful cases yield approximately the same numerical result as Einstein's theory, then how is Newton's theory not an approximation of Einstein's theory?
  - ignoramous 7y ago
    Consider the argument from the point of mathematics of it all, and the entire genre of relativity which is a vehement departure from classical physics. Newton's model captures the essence but isn't the eternal truth. Relativity proved that. Today, singularities have been proven to exist that point to missing pieces in Einstein's theory. The point is, simpler models are a good approximation even though they don't hold true under scrutiny, so, at what point do we stop obsessing over details and complex models professionals come up with or the policy-makers seek because surely there's law of diminishing returns at play here?
    - heavenlyblue 7y ago
      The law of diminishing returns only works in linear spaces. When you reach that point the only progress you can make is to create a better model of reality that would include these wraps.

by FabHK 7y ago

ignoramous 7y ago

> I don’t understand what you’re saying. I think what GP means is, leaving it upto professionals alone is a recipe for disaster because of the inherent corruption, greed, biases, and prejudices at play. > So what are you advocating? Not speaking for GP, but simpler models are more likely to be a good approximation and more than enough, anyway [0]? Simplicity helps because it stops the pundits and politicians from sort of running away with it? [0] Newton's theory of gravitation has been supplanted by Einstein's theory of relativity and yet Newton's theory remains generally "empirically adequate". Indeed, Newton's theory generally has excellent predictive power. Yet Newton's theory is not an approximation of Einstein's theory. For illustration, consider an apple falling down from a tree. Under Newton's theory, the apple falls because Earth exerts a force on the apple—what is called "the force of gravity". Under Einstein's theory, Earth does not exert any force on the apple. Hence, Newton's theory might be regarded as being, in some sense, completely wrong but extremely useful (The usefulness of Newton's theory comes partly from being vastly simpler, both mathematically and computationally, than Einstein's theory). https://en.wikipedia.org/wiki/All_models_are_wrong https://en.wikipedia.org/wiki/All_models_are_wrong

FabHK 7y ago
> because of the inherent corruption, greed, biases, and prejudices at play. You and I must be thinking of different professionals. At any rate, here are two very very very simple models of this epidemic: a) cases will grow linearly, b) cases will grow exponentially. Super simple. extremely different outcome. Now, one still has to make policy decisions. I think the solution is not fewer professionals, but more and better professionals.
- samatman 7y ago
  Both of these are wrong, and the exponential one becomes more wrong faster, while being a better match for the beginning of the curve. Exponential processes don't exist in nature, they always break into some other curve at some point.
  - jhayward 7y ago
    This is a useless bit of pedantry. The exponential portion of the sigmoid curve is the only part that matters to human health, survival, and economic well-being.
    - samatman 7y ago
      Then why, pray tell, is the title of the article we are discussing not "Forecasting exponential curves is hard"? The entire point is that forecasting exponentials is easy but becomes badly wrong at some point and that point is difficult to forecast
    - nl 7y ago
      No it's absolutely not!! Epidemics are (more) properly modelled by the Gompertz function[1], and the position of the "transition" between the exponential portion and non-exponential points it the important point. That is exactly what the person you are replying to is saying ("they always break into some other curve at some point."). [1] https://en.wikipedia.org/wiki/Gompertz_function https://en.wikipedia.org/wiki/Gompertz_function
      - BaronSamedi 7y ago
        Is the Gompertz function the function behind the standard "epi curve"? It appears from the CDC web site and other places that the epi curve is the standard way epidemics are modeled. The CDC even has a simple tutorial for creating them: https://www.cdc.gov/training/quicklearns/createepi/index.html https://www.cdc.gov/training/quicklearns/createepi/index.htm...
haneefmubarak 7y ago
If Einstein's theory roughly says that massive objects deform space proportional to their mass, the effect of which is that massive objects (all else held equal) will tend to move towards each other more so than they would otherwise; meanwhile Newton's theory says that massive objects attract each other proportional to the product of their masses divided by the square of their distance; and Newton's theory does in the vast majority of useful cases yield approximately the same numerical result as Einstein's theory, then how is Newton's theory not an approximation of Einstein's theory?
- ignoramous 7y ago
  Consider the argument from the point of mathematics of it all, and the entire genre of relativity which is a vehement departure from classical physics. Newton's model captures the essence but isn't the eternal truth. Relativity proved that. Today, singularities have been proven to exist that point to missing pieces in Einstein's theory. The point is, simpler models are a good approximation even though they don't hold true under scrutiny, so, at what point do we stop obsessing over details and complex models professionals come up with or the policy-makers seek because surely there's law of diminishing returns at play here?
  - heavenlyblue 7y ago
    The law of diminishing returns only works in linear spaces. When you reach that point the only progress you can make is to create a better model of reality that would include these wraps.