Median Statistics and the Mass Density of the Universe

We use weighted mean and median statistics techniques to combine individual estimates of ΩM0, the present mean mass density in non-relativistic matter, and determine the observed values and ranges of ΩM0 from different combinations of data. The derived weighted mean ΩM0 values are not good representatives of the individual measurements, under the assumptions of Gaussianity and negligible correlation between the individual measurements. This could mean that some observational error bars are under-estimated. Discarding the most discrepant ∼ 5 % of the measurements generally alleviates but does not completely resolve this problem. While the results derived from the different combinations of data are not identical, they are mostly consistent, and a reasonable summary of the median statistics analyses is 0.2 . ΩM0 . 0.35 at two standard deviations. Subject headings: cosmology: cosmological parameters—cosmology: observation—methods: statistics—methods: data analysis—large-scale structure of the universe