R help - May 2005 - formula restriction in multinom?

Good Day: When I used: 
multinom(formula = Y ~ X1 + X2 + X3 + X1:X2 + X1:X3 + X3:X2 + X1^2 + X2^2 +
X3^2, data = DATASET),
I get estimates and AIC for the model containing main effects and
interactions only (no squared terms)...and FYI, all predictors are
continuous. Is this "normal" behavior? If I run this in S-Plus I get
estimates and AIC for the model containing all terms(including the squared
terms).

   Thanks,
   Mark Berry




LEGAL NOTICE\ Unless expressly stated otherwise, this messag...{{dropped}}

Note: multinom() is in nnet package.

In any case, the answer is, yes, this is "normal" behavior:

x^2 <==> x:x <==> x in S language linear model notation. So if you
want a
quadratic you must use I(x^2). S-Plus does this silently, but it is not
required by the language definition.

-- Bert Gunter
Genentech Non-Clinical Statistics
South San Francisco, CA
 
"The business of the statistician is to catalyze the scientific learning
process."  - George E. P. Box
 
 
> -----Original Message-----
> From: r-help-bounces at stat.math.ethz.ch 
> [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Berry, Mark R
> Sent: Monday, May 09, 2005 11:33 AM
> To: 'r-help at stat.math.ethz.ch'
> Subject: [R] formula restriction in multinom?
> 
> Good Day: When I used: 
> multinom(formula = Y ~ X1 + X2 + X3 + X1:X2 + X1:X3 + X3:X2 + 
> X1^2 + X2^2 +
> X3^2, data = DATASET),
> I get estimates and AIC for the model containing main effects and
> interactions only (no squared terms)...and FYI, all predictors are
> continuous. Is this "normal" behavior? If I run this in S-Plus I
get
> estimates and AIC for the model containing all 
> terms(including the squared
> terms).
> 
>    Thanks,
>    Mark Berry
> 
> 
> 
> 
> LEGAL NOTICE\ Unless expressly stated otherwise, this 
> messag...{{dropped}}
> 
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