[R] Trying something for fun...

[Charles C. Berry]

On Fri, 21 Aug 2009, Noah Silverman wrote:

> Hi,
>
> For fun, I'm trying to throw some horse racing data into either an svm or lrm 
> model.  Curious to see what comes out as there are so many published papers 
> on this.
>
> One thing I don't know how to do is to standardize the probabilities by race.


This sounds closer to the conditional logit model.

However, if I recall correctly there is an assumption that in the models 
of choice literature is stated something like 'independence of 
alternatives that are unavailable'.  That assumption might not hold in a 
horse race where the speed at which a horse runs may depend on what horses 
she is running against.

See

 	?survival:::clogit

and

@article{mcfadden1974conditional,
   title={{Conditional logit analysis of qualitative choice behavior}},
   author={McFadden, D.},
   journal={Frontiers in econometrics},
   volume={8},
   pages={105--142},
   year={1974}
}


BTW, Professor McFadden has a quintessentially American biography:

  http://nobelprize.org/nobel_prizes/economics/laureates/2000/mcfadden-autobio.html

He mentions his personal background in farming and awards won for his 
'sheep and geese', but alas does not mention horses or racing.

HTH,

Chuck

>
> For example, if I train an LRM on a bunch of variable I get a model.  I can 
> then get probability predictions from the model.  That works.
>
> It seems to me, that for a given race (8-12 horses) the probabilites of my 
> predictions should sum to one.
>
> 1) Is there some way to train the LRM to evaluate and then model the 
> subsequent date "per race"??  (Perhaps indicate some kind of grouping 
> variable?
>
> 2) Alternately, if I just run my data through a "standard" LRM, is there some 
> way to then "normalize" the probabilities in a correct way for each upcoming 
> race?
>
> I've done some extensive research in this area and would be willing to 
> discuss more details offline with someone if they could contribute to the 
> process.
>
> Thanks!!
>
> -N
>
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Charles C. Berry                            (858) 534-2098
                                             Dept of Family/Preventive Medicine
E mailto:cberry at tajo.ucsd.edu	            UC San Diego
http://famprevmed.ucsd.edu/faculty/cberry/  La Jolla, San Diego 92093-0901