  We present the estimates of the order $O(\alpha^{4}_{s})$ QCD corrections to
$R(s)$, $R_{\tau}$ and to the deep-inelastic scattering sum rules, namely to
the non-polarized and polarized Bjorken sum rules and to the Gross-Llewellyn
Smith sum rule. The estimates are obtained in the $\overline{MS}$-scheme using
the principle of minimal sensitivity and the effective charges approach.
