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Re: st: Convert SAS code to STATA


From   "JVerkuilen (Gmail)" <jvverkuilen@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Convert SAS code to STATA
Date   Sat, 22 Sep 2012 17:29:20 -0400

Before venturing into -margins-, I'd make sure that SAS and Stata are
fitting the same model (up to the inevitable differences in say the
third or fourth decimal place), even if they're not identified quite
the same way. This may not be straightforward as I seem to recall SAS
puts out rather different fit statistics than Stata.



On Sat, Sep 22, 2012 at 3:59 PM, Marquis Hawkins
<marquishawkins82@hotmail.com> wrote:
> My goal was to get change per year.  with SAS using the contrast "-0.333 0.333 0 0 0 0 ", this compares the average change in GFR over three years between the two groups.  I'm not sure how to do this in STATA.
>
> In SAS I using the following:
>
> PROC mixed data= habc.habclong covtest;
> class habcid ckd1 time;
> model gfr = ckd1*time/solution ;
> repeated time/type=un subject=habcid;
> estimate 'avg change/year between baseline and year 3 for grp 1' ckd1*time -0.333 0.333 0 0 0 0 ;
> estimate 'avg change/year between year 3 and year 10 for grp 1' ckd1*time 0 -0.143 0.143 0 0 0 ;
> estimate 'avg change/year between baseline and year 3 for grp 2' ckd1*time 0 0 0 -0.333 0.333 0 ;
> estimate 'avg change/year between year 3 and year 10 for grp 2' ckd1*time 0 0 0 0 -0.143 0.143 ;
> where inclusion=1;
> run;
>
> When I use the following STATA code:
>
> xi: xtmixed gfr totpa3cat##time if inclusion==1 ///
>  || habcid: , noconstant residuals(uns, t(time)) nolog reml
>
> margins totpa3cat time totpa3cat##time if inclusion==1, contrast
>
> It does not give me the same information.  It only gives me the mean GFR at each time point by CKD group.  I can't put in the contrast here the same as I do it in SAS.  Any advice?
>
>
>
> ----------------------------------------
>> Date: Sat, 22 Sep 2012 12:11:52 -0400
>> Subject: Re: st: Convert SAS code to STATA
>> From: jvverkuilen@gmail.com
>> To: statalist@hsphsun2.harvard.edu
>>
>> On Sat, Sep 22, 2012 at 11:59 AM, Marquis Hawkins
>> <marquishawkins82@hotmail.com> wrote:
>> > Hi,
>> >
>> > Does anyone know how to convert this SAS code to STATA?
>> >
>> >
>> > PROC mixed data= habc.habclong covtest;
>> > class habcid ckd1 time;
>> > model gfr = ckd1*time/solution ;
>> > repeated time/type=un subject=habcid;
>> > estimate 'avg change/year between baseline and year 3 for grp 1' ckd1*time -0.333 0.333 0 0 0 0 ;
>> > estimate 'avg change/year between year 3 and year 10 for grp 1' ckd1*time 0 -0.143 0.143 0 0 0 ;
>> > estimate 'avg change/year between baseline and year 3 for grp 2' ckd1*time 0 0 0 -0.333 0.333 0 ;
>> > estimate 'avg change/year between year 3 and year 10 for grp 2' ckd1*time 0 0 0 0 -0.143 0.143 ;
>> > where inclusion=1;
>> > run;
>>
>> PROC MIXED would go over to -xtmixed-.
>>
>> The "estimate" commands would be post-estimation calls to -margins-.
>>
>> The "class" statement would be done using Stata factor commands (i.,
>> etc.) or -xi-.
>>
>> "Repeated" specifies the random structure. That's the part you'll have
>> to do a little work to map to the right specification but it looks
>> like you wanted an unstructured covariance matrix and that should be
>> pretty straightforward to do.
>>
>>
>> --
>> JVVerkuilen, PhD
>> jvverkuilen@gmail.com
>>
>> "Out beyond ideas of wrong-doing and right-doing there is a field.
>> I'll meet you there. When the soul lies down in that grass the world
>> is too full to talk about." ---Rumi
>> *
>> * For searches and help try:
>> * http://www.stata.com/help.cgi?search
>> * http://www.stata.com/support/statalist/faq
>> * http://www.ats.ucla.edu/stat/stata/
>
> *
> *   For searches and help try:
> *   http://www.stata.com/help.cgi?search
> *   http://www.stata.com/support/statalist/faq
> *   http://www.ats.ucla.edu/stat/stata/



-- 
JVVerkuilen, PhD
jvverkuilen@gmail.com

"Out beyond ideas of wrong-doing and right-doing there is a field.
I'll meet you there. When the soul lies down in that grass the world
is too full to talk about." ---Rumi
*
*   For searches and help try:
*   http://www.stata.com/help.cgi?search
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/


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