Statistical power balance modeling originally applied to reverberation chamber design has the potential to benefit a much wider range of EMC and signal integrity applications. This paper will review the physics and statistical foundations of Hill’s model for reverberation chambers, the extension to multiply connected cavities and the coupling to multi-conductor cable currents inside the cavity field. The paper will then introduce a new unconditional probability density function formulation, further expanding the model to handle the statistics of electrically small cavities and the incorporation of uncertainty in the cavity Q factor.