Programming the statistical procedures from SAS

PROC MIXED - Random statement uncertainty

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New Contributor
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PROC MIXED - Random statement uncertainty

[ Edited ]

I am analyzing a data set.

 

I have 3 x 4 x 4 design.

Three treatments with four doses for each treatment and four sample time points for each dose. The samples are individual samples at different times (not repeated samples).

 

I am using Proc Mixed as under

 

proc mixed; 
class group dose time;
model e=dose|group|time/ outp=new;
random 

 

data residy; set new;
proc plot;
plot resid*pred;
proc univariate plot normal;
var resid;
run;
 
I am not sure what should be my  "random" statement.
 
I will appreciate any help. Thanks
PROC Star
PROC Star
Posts: 403

Re: PROC MIXED - Random statement uncertainty

[ Edited ]

If the observations are independent--if there is no clustering, or blocking, or repeated measures on the same subject--and if the homogeneity of variances assumption is met, then there is only one source of variance in your design (which will be estimated as residual variance) and you do not need a RANDOM statement. The MIXED procedure works just fine without a RANDOM statement.

 

New Contributor
Posts: 2

Re: PROC MIXED - Random statement uncertainty

Many thanks. It was of great help.

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