can someone point me to where SAS or a SAS user discusses how procedures with an obligate residual variance term (eg MIXED, HPMIXED) address situations where, due to an absence of replication, an interaction variance is confounded with what these procs call residual variance? in such a situation and when the levels of the factors are treated as random, i obtain estimates for both the interaction term and the residual variance that are roughly half that supplied for the residual variance when the confounded/aliased term is omitted. here's example code: ods select off; proc hpmixed data=A; class reader structure; model agenum = structure / s; random reader / s; random structure*reader / s; ods output covparms=covparms; run; ods select all; proc print data=covparms; run; * as above except omitting structure*reader term; ods select off; proc hpmixed data=A; class reader structure; model agenum = structure / s; random reader / s; *random structure*reader / s; ods output covparms=covparms2; run; ods select all; proc print data=covparms2; run;
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