We consider a simple model, the two-site small-polaron system, and show that its properties can be characterized by a master equation which is in accordance with recent quantum statistical theories of macroscopic observables. It is shown by a combination of formal and numerical analyses that the model is an example of a system describable by the lowest-order term in the expansion of the kernel of the master equation in powers of the ratio of the average polaron-phonon interaction energy to the microscopic phonon energy. We discuss the relevance of the method to actual physical systems.