[R-sig-ME] lme interaction result strange

[Ista Zahn]

Hi Charles,

You can print and assign contrasts in R using the contrasts function.
See ?contrasts for details. You may also wish to look at ?contr.SAS

HTH,
Ista

On Tue, May 1, 2012 at 1:53 PM, Charles Determan Jr <deter088 at umn.edu> wrote:
> Thank you for your response Ista.  Do you have a recommendations how I might
> address variation in the contrasts?
>
> Regards,
> Charles
>
>
> On Tue, May 1, 2012 at 12:51 PM, Ista Zahn <istazahn at gmail.com> wrote:
>>
>> Hi Charles,
>>
>> My first guess is that you have (a) categorical variable(s) in your
>> predictors, and that the contrasts in SAS are different than those in
>> R.
>>
>> Best,
>> Ista
>>
>> On Tue, May 1, 2012 at 1:39 PM, Charles Determan Jr <deter088 at umn.edu>
>> wrote:
>> > Dear R users,
>> >
>> > I have been working on replicating some linear mixed models from SAS.
>> >  The
>> > first one matches perfectly when the SAS model is simple with the three
>> > separate factors.
>> >
>> > fit=lme(var~group+Event_name+Died,
>> >    data=liv34,
>> >    random=~1|ID)
>> > anova.lme(fit, type="marginal", adjustSigma=F)
>> >
>> > However, once I put an interaction into the formula the values don't
>> > match.
>> >
>> > fit=lme(var~group+Event_name+Died+Event_name*Died,
>> >    data=liv34,
>> >    random=~1|ID)
>> > anova.lme(fit, type="marginal", adjustSigma=F)
>> >
>> >                          numDF denDF     F-value      p-value
>> > (Intercept)               1        91       111.20483  <.0001
>> > group                      1        23        0.46632     0.5015
>> > Event_name            5        91        1.14042     *0.3449*
>> > Died                       1        23        0.50989    * 0.4824*
>> > Event_name:Died     5       91        1.10436     0.3637
>> > Done.
>> >
>> > The numbers *bold* don't match up.  They should be approximately .0290
>> > and
>> > .1318 respectively.  The other two are still exact matches.  I know
>> > looking
>> > for exact matches is ambitious but the numbers should be at least
>> > similar
>> > that the conclusions don't change so drastically.
>> >
>> > Any thoughts as to why this discrepancy is happening would be most
>> > appreciated.
>> >
>> > Regards,
>> >
>> > Charles
>> >
>> >        [[alternative HTML version deleted]]
>> >
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>
>