Essbase member formula formula pulling in 2 quarter average across years

@ISMBR("Q1"))

I am working on a member formula on the accounts dimension which pulls in a quaterly average from the current quarter + prior quarter divided bt 2.

my problem is in Q1 how do I pull in q4 from the prior year?

IF  (@ISMBR("Q1"))

ELSEIF  (@ISMBR("Q2"))          
"Stat_AvgNetAssets" = ("Q1"->"PPENET" + "Q1"->"A141000" + "Q2"->"PPENET" + "Q2"->"PPENET" + "Q2"->"A141000")/2;          
ELSEIF  (@ISMBR("Q3"))
"Stat_AvgNetAssets" = ("Q2"->"PPENET" + "Q2"->"A141000" + "Q3"->"PPENET" + "Q2"->"PPENET" + "Q3"->"A141000")/2;       
ELSEIF  (@ISMBR("Q4"))          
"Stat_AvgNetAssets" = ("Q3"->"PPENET" + "Q3"->"A141000" + "Q2"->"PPENET" + "Q4"->"PPENET" + "Q4"->"A141000")/2;