R help - Aug 2009 - Trying something for fun...

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.

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

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