Ghost-gluon running coupling, power corrections, and the determination of Λ(MS)over-bar

We compute a formula including operator-product expansion power corrections to describe the running of a QCD coupling nonperturbatively defined through the ghost and gluon dressing functions. This turns out to be rather accurate. We propose the ``plateau'' procedure to compute Delta(MS) over bar from the lattice computation of the running coupling constant. We show a good agreement between the different methods which have been used to estimate Lambda (Nf= 0)((MS) over bar). We argue that Lambda(MS) over bar or the strong coupling constant computed with different lattice spacings may be used to estimate the lattice spacing ratio.