Comparing transitive to non-transitive object immutability

Many programming languages provide features that express restrictions on which data structures can be changed. For example, C++ includes const and Java includes final. Languages that are in widespread use typically provide non-transitive immutability: when a reference is specified to be immutable or read-only, the object referenced can still reference mutable structures. However, some languages, particularly research languages, provide transitive immutability, in which immutable objects can only reference other immutable objects (with some exceptions). We are designing a lab study of programmers to elucidate the differences in programmer effectiveness between these two approaches.