A combination by the LEP QCD Working Group of $\alpha_{s}$ values derived from event shape variables at LEP

The LEP QCD Working Group has produced a combination of alpha /sub s/ values derived from event-shape distributions. The distributions are measured at scales below the mass of the Z boson up to 206 GeV. Values of alpha /sub s/ are all extracted using the consistent application of O( alpha /sub s//sup 2/)+NLLA predictions with the modified Log(R) matching scheme. A combined alpha /sub s/ is obtained for each experiment and observable using at least two experiments in each case for energies above at ad above the mass of the Z boson. A consistent treatment and controlled breakdown is made of the sources of uncertainty on the input values. The combined best value for alpha /sub s/(M/sub Z/) = 0.11 +or- 0.003 +or- 0.003. The dominant uncertainty is theoretical, due to the effects of missing higher order contributions.