Complex sentence: Thus, the deinstitutionalisation that took place in the United States has been considered by some to be more of a "transitionalisation", that is, a transition from a mental institution to a more human community centered facility.
Split into simpler sentences: Thus, the deinstitutionalisation that took place in the United States has been considered by some to be more of a "transitionalisation". That is to say, a transition from a mental institution to a more human community centered facility.