According to the theory of electron-electron scattering the ratio A/γ contains indeed several non-universal factors, including the square of the strength of the effective electron-electron interaction. Since in general the interactions differ in nature from one group of materials to another, the same values of A/γ are only expected within a particular group. In 2005 Hussey proposed a re-scaling of A/γ to account for unit cell volume, dimensionality, carrier density and multi-band effects. In 2009 Jacko, Fjaerestad, and Powell demonstrated f dx (n)A/γ to have the same value in transition metals, heavy fermions, organics and oxides with A varying over 10 orders of magnitude, where f dx (n) may be written in terms of the dimensionality of the system, the electron density and, in layered systems, the interlayer spacing or the interlayer hopping integral.