  We formalize the hidden measurement approach within the very general notion
of an interactive probability model. We narrow down the model by assuming the
state space of a physical entity is a complex Hilbert space and introduce the
principle of consistent interaction which effectively partitions the space of
apparatus states. The normalized measure of the set of apparatus states that
interact with a pure state giving rise to a fixed outcome is shown to be in
accordance with the probability obtained using the Born rule.
