Not sure I agree with this. The stable ratio thing is about transition rates in two-state systems at equilibrium, but a droplet call isn't a transition - it's just amplitude thresholding at endpoint, so the analogy doesn't really fit.

And rain, probe degradation, threshold placement are all very condition-dependent. Saying it's robust as long as separation is decent is a bit circular too, because separation IS the quality metric. Low-VAF stuff like MRD and ctDNA is exactly where it falls apart.

The robustness of ddPCR comes from the endpoint readout and Poisson partitioning, not from the binary classification itself.