  A QCD analysis of the world data on polarized deep inelastic scattering is
presented in next--to--leading order, including the heavy flavor Wilson
coefficient in leading order in the fixed flavor number scheme. New
parameterizations are derived for the quark and gluon distributions and the
value of $\alpha_s(M_z^2)$ is determined. The impact of the variation of both
the renormalization and factorization scales on the distributions and the value
of $\alpha_s$ is studied. We obtain $\alpha_s^{\rm NLO}(M_Z^2) =
0.1132~~\begin{array}{l} + 0.0056 \\ -0.0095 \end{array}$. The first moments of
the polarized twist--2 parton distribution functions are calculated with
correlated errors to allow for comparisons with results from lattice QCD
simulations. Potential higher twist contributions to the structure function
$g_1(x,Q^2)$ are determined and found to be compatible with zero both for
proton and deuteron targets.
