  We performed NLO QCD analysis of the nonsinglet part of the combined
SLAC/BCDMS data on $F_2$ with the extraction of $\alpha_s$ and high twist
contribution. It was shown that the value of $\alpha_s$ obtained in the
analysis is sensitive to the statistical inference procedures dealing with
systematic errors on the data. The fit with the complete account of
point-to-point correlations of the data gave the value of
$\alpha_s(M_Z)=0.1180\pm0.0017 (68% C.L.)$, to be compared with the previously
reported value of $\alpha_s(M_Z)=0.113\pm0.003 (99% C.L.)$. This new value of
$\alpha_s$ is compatible with the LEP measurements and the world average. The
high twist contribution being strongly anti-correlated with the value of
$\alpha_s$ became lower than it was previously reported.
