Binned Hubble parameter measurements and the cosmological deceleration-acceleration transition

Weighted mean and median statistics techniques are used to combine 23 independent lower redshift, z<1.04, Hubble parameter, H(z), measurements and determine binned forms of H(z). When these are combined with 5 higher redshift, 1.3≤z≤2.3, H(z) measurements the resulting constraints on cosmological parameters, of three cosmological models, that follow from the weighted-mean binned data are almost identical to those derived from analyses using the 28 independent H(z) measurements. This is consistent with what is expected if the lower redshift measurements errors are Gaussian. Plots of the binned weighted-mean H(z)/(1+z) versus z data are consistent with the presence of a cosmological deceleration–acceleration transition at redshift zda=0.74±0.05 [30], which is expected in cosmological models with present-epoch energy budget dominated by dark energy as in the standard spatially-flat ΛCDM cosmological model.