An analysis of the collapse postulate for a two‐system situation is given. Asuperpositionof product wavefunctions is used to define a homogeneous ensemble and amixtureof product wavefunctions to define a heterogeneous ensemble. The expectation value of a product of operators is considered, such that the first has nonzero matrix elements only for states pertaining to system 1 and the second only for states of system 2. A condition is derived for the expectation values as averaged over the two ensembles to be identical, i.e., for the collapse postulate to be unnecessary. The result is applied to (i) the measurement problem, (ii) the design of a possible experiment to test for the validity of the collapse postulate, and (iii) to the Einstein–Podolsky–Rosen (EPR) example. In many cases the collapse postulate is not needed in the ensemble picture. When it is needed it is equivalent to a random phase assumption of a kind which is usually employed in statistical mechanics.