[R] Effects library LSM decimal place errors

Nieves Felipe nieves.felipe at gmail.com
Fri Jul 16 05:41:41 CEST 2010


G'day,
I'm calculating LSM for the following model, and am finding that R and
SAS give different answers.
Whilst the error is at the second or third decimal, the percentage
error can be quite large.

I'm using the effects library (Version: 2.0-10) on R 2.11.1 in the
following manner:

options(contrasts=c("contr.helmert","contr.poly"))
aov2<-glm(log(y+.01)~covar+var1:var3+var2:var3+var1+var2+var3,data=mydat,weights=w)
mod<-effect("var1",aov2)
cbind(mod$fit, mod$se)

R gives the following values for var1:
    LSM             SE
 -4.080362 0.06692946
 -4.221714 0.10233130

The same problem gives the following values in SAS:

var1 ln_y             Error
-4.10699540 0.06879095
-4.21943501 0.10096482

The following is my SAS code:

PROC IMPORT OUT= WORK.dat
     DATAFILE= "C:\Documents and Settings\nxf\Desktop\mydat.xls"
     DBMS=EXCEL REPLACE; GETNAMES=YES;
     MIXED=NO; SCANTEXT=YES; USEDATE=YES; SCANTIME=YES;
RUN;
proc contents data=dat;
run;
data dum;
	set dat;
	ln_y = log(y+0.01);
run;
proc glm data=dum;
  title2 'test';
  weight w;
  class var1 var2 var3;
  model  ln_y = covar var1 var2 var3 var1*var3 var2*var3;
  lsmeans var1 var2 var3 var1*var3 var2*var3 /out=LSMeffect stderr;
run;quit;
proc print data=LSMeffect;
run;
proc export data=LSMeffect outfile='C:\Documents and
Settings\nxf\Desktop\sas1.xls'
            DBMS=EXCEL2000 replace;
run;

I've been using R for about 4 months, apologies if this has a simple
solution I'm unaware of. I'm completely new to SAS.
Many thanks in advance,

Nieves Felipe.


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