Ghost-gluon running coupling, power corrections and the determination of   $\Lambda_{\bar {\rm MS}}$
  We compute a formula including OPE power corrections to describe the running of a QCD coupling non-perturbatively defined through the ghost and gluon dressing functions. This turns out to be rather accurate. We propose the ``{\it plateau}''-procedure to compute $\Lambda_{\bar{\rm MS}}$ from the lattice computation of the running coupling constant. We show a good agreement between the different methods which have been used to estimate $\Lambda_{\bar{\rm MS}}^{N_f=0}$. We argue that $\Lambda_{\bar{\rm MS}}$ or the strong coupling constant computed with different lattice spacings may be used to estimate the lattice spacing ratio. 
Ph. Boucaud, F. De Soto, J.P. Leroy, A. Le Yaouanc, J. Micheli, O.   P\`ene, J. Rodr\'iguez-Quintero