H_0 and Odds on Cosmology

Recent observations by the Hubble Space Telescope of Cepheids in the Virgo cluster imply a Hubble Constant $H_0=80\pm 17$\ km/sec/Mpc. We attempt to clarify some issues of interpretation of these results for determining the global cosmological parameters $\mathrm{\Omega }$ and $\mathrm{\Lambda }$. Using the formalism of Bayesian model comparison, the data suggest a universe with a nonzero cosmological constant $\mathrm{\Lambda }>0$, but vanishing curvature: $\mathrm{\Omega }+\mathrm{\Lambda }=1$.