2 groups with different sample periods

[johnmacey]

I use Popan for CMR data. I have 2 groups, both with identicle varibles collected. However I have one group with 13 seasons of data and the 2nd group with 12 seasons of data. The second group did not get collected in the 13th year due to financial constraints. CAn I compute them together. Is there some way I can distinguish the difference.