  We show that standard next-to-leading order (NLO) perturbative QCD analyses
used to extract $\alpha_{s}$ from LEP data do not serve to disentangle the
completely unknown renormalization scheme (RS) invariant next-NLO (NNLO) and
higher-order uncalculated corrections from those dependent on the
renormalization scale in a predictable manner. The resulting quoted values of
$\alpha_{s}(M_{Z})$ $(\tilde{\Lambda}_{\overline{MS}})$ with attendant scheme
dependence uncertainties therefore reflect the ad hoc way in which they were
extracted, rather than the actual values of these parameters. Choosing the
scale so that the NLO coefficient vanishes (effective charge scheme) exposes
the relative size of these unknown RS invariant higher order terms. They are
seen to be sizeable for some of the LEP observables, indicating that they must
be estimated if $\tilde{\Lambda}_{\overline{MS}}$ is to be determined reliably.
This can be accomplished either from NNLO calculations, at present only
available for the hadronic width of the $Z^{0}$ ($R_{Z}$), or
non-perturbatively by writing the RS-invariant uncertainty in $\tilde{\Lambda}$
in terms of the running ${dR(Q)}/{d \ln Q}$ of the observable R(Q) with energy
using an effective charge formalism. The NNLO calculations for $R_{Z}$ and LEP
data supplemented by lower energy PETRA data lead to
$\tilde{\Lambda}^{(5)}_{\overline{MS}}=287 \pm 100$ MeV. We also
