Between Occasion variability

Dear Nonmem users, I am trying to model data from 4 studies. These were multi center studies conducted at different times. 2 of these 4 studies had a crossover design with 4 dose levels (occasions). However not all individuals had all dose levels. Most of the individuals had 3 occasions out of 4 dose levels. 2 studies were a crossover design with IV and SC routes of administration. I was wondering if I could still estimate the BOV (between occasion variability) when I was analyzing the complete data simultaneously. I have previously analyzed data from a single study with BOV (with all individuals having all occasions) . But I have never done this with data from studies conducted at different times at different sites with some having more than one occasion and some just one occasion. If yes, do I just estimate the BOV in the same way as for a single study in the following way ?? ID Study occ time DV amt rate EVID 1 1 1 0 0 3 1 1 1 1 1 1 5 0 0 0 1 1 2 0 0 3 1 1 1 1 2 1 4.5 0 0 0 1 1 3 0 0 3 1 1 1 1 3 1 5.5 0 0 0 2 2 1 0 0 2 2 1 2 2 1 0 7 0 0 0 3 2 1 0 0 2 2 1 3 2 1 0 7.5 0 0 0 4 3 1 0 0 2 2 1 4 3 1 0 7 0 0 0 OC1=0 IF(OCC.EQ.1) OC1=1 OC2=0 IF(OCC.EQ.2) OC2=1 OC3=0 IF(OCC.EQ.3) OC3=1 OC4=0 IF(OCC.EQ.4) OC4=1 BOV1=ETA(6)*OC1+ETA(8)*OC2+ETA(10)*OC3+ETA(12)*OC4 BOV2=ETA(7)*OC1+ETA(9)*OC2+ETA(11)*OC3+ETA(13)*OC4 CL=TVCL*EXP(ETA(1)+BOV1) V2=TVV2*EXP(ETA(2)+BOV2) Any help or suggestions are appreciated Thanks in advance --Navin