  We present a novel approach to the analysis of the normal state in-plane
$\sigma_{ab}$ and out-of-plane $\sigma_{c}$ conductivities of anisotropic
layered crystals such as oxygen deficient $YBa_{2}Cu_{3}O_{x}$. It can be shown
that the resistive anisotropy is determined by the ratio of the phase coherence
lengths in the respective directions; i.e.,
$\sigma_{ab}/\sigma_c=\ell_{ab}^2/\ell_c^2$. From the idea that at all doping
levels and temperatures $T$ the out-of-plane transport in these crystals is
incoherent, follows that $\ell_c$ is T-independent, equal to the spacing
$\ell_0$ between the neighboring bilayers. Thus, the T-dependence of
$\ell_{ab}$ is given by the measured anisotropy, and $\sigma_{ab}(\ell_{ab})$
dependence is obtained by plotting $\sigma_{ab}$ vs
$\ell=(\sigma_{ab}/\sigma_c)^{1/2}\ell_0$. The analysis of several single
crystals of $YBa_{2}Cu_{3}O_{x}$ ($6.35<x<6.93$) shows that for all of them
$\sigma_{ab}(\ell)$ is described by a universal dependence
$\sigma_{ab}/\bar\sigma =f(\ell/\bar\ell)$ with doping dependent parameters
$\bar\sigma$ and $\bar\ell$.
