Wednesday, October 19, 2022

It should be true

I don't know if it's true but it should be.  Either way, it's believable and hysterical.

Joe Martino tells TOF that "One of the most horrible examples I ever encountered was the use of a Cobb-Douglas Production Function to predict the effectiveness of bombing the Ho Chi Minh trail. When I first saw the model it fairly screamed 'wrong!' But the people who put it together saw nothing wrong with it."

A Cobb-Douglas Production Function, a quick wiki search discovers, is a model designed to predict input-output relationships in manufacturing.  I'll assume that my readers understand my amusement.

The article from which the quote came, a general overview of bad statistical modeling: 

https://tofspot.blogspot.com/2014/03/americas-next-top-model-part-ii.html 


The article which led me to the aforementioned article, a review of a study in which 70 teams given the same data and same hypothesis came up with over 1,000 models, none of which produced the same result:

https://www.wmbriggs.com/post/43052/

 

And finally, the article I'll be reading after I finish the first listed above, a review of the same study by a different author:

https://wattsupwiththat.com/2022/10/17/a-hidden-universe-of-uncertainty/ 


And in case you haven't been following along, the synopsis of the case against modeling:

  1. Models say what they are designed to say
  2. Models make significant numbers of assumptions, all of which change the results of the model
  3. People assume that a small p-value means the model is accurate (hint: all the studies in the example discussed by Briggs had wee p-values, even the ones that contradicted each other in results)

3 comments:

John Wilder said...

Models should be as simple as possible, but if you use the wrong one, it will always, (always!) give the wrong answer.

Anonymous said...

Thecpurpose of models is to provide insight, not answers.

Anonymous said...

That was me above too. In my profession, military modeling, i have seen this before and discovered that the US military love deluding themselves. Out entire defense bedget is based on old cold war dynamics of fantasy war in models, updated to reflect budget cuts and budget gluts. It has very little connection to reality. Only 10 years ago, the us army was basing its biggest big ticket items on a premise of fighting North Korea. NORTH FING KOREA. We shifted to Russia-China becase no one could say north korea with a straight face. Now even saying Russia will get you ignored in high places. We need our fantasy enemies. You can't justify f-35s on a theory of fighting ISIS.
--generic