We know that the so-called Matthiessen's rule is valid when different scattering processes can be considered independent. In this case it says that the total resistivity R is a sum of different sources, that is (e.g., for two processes) R=R1+R2. When there is a substantial correlation between these scattering processes, this rule is not applicable anymore. Quite often (like in the systems described by hopping conductivity), in such situations a better solution would be to add conductivities (1/R) instead of resistivities. That is the total resistivity in this case should read: R=1/(1/R1+1/R2). Perhaps these two situations could be linked to probability theory. For independent events we have the Matthiessen's rule and for correlated events (conditional probability?) its violation. My question: is there an analog of the Matthiessen's rule violation for magnetization (or susceptibility) when, instead of adding (say) susceptibilities K=K1+K2 coming from different (independent) magnetic sources (which is usually the case), for explaining the experimental data we should be using the inverse scheme with the total susceptibility given by K=1/(1/K1+1/K2)?