A strange thought just occurred to me. There are always people leaving one denomination (or even religion) and entering another. I wonder if the conversion and apostacy rates could be modelled as molecules evaporating from one liquid and condensing in another. Members since birth and converts that either never leave or leave only after a long time could be modelled as members of solids. In these models, temperatures would be indicative of scandal, heresy, revival, reform, and other major causes of movement between denominations. Also, different groups would have different state transition temperatures, reflecting relative cohesiveness.
Thoughts?