A recent study of the rotation of the plane of polarization of light from 160 cosmological sources claims to find significant evidence for cosmological anisotropy .
We point out methodological weaknesses of that study , and reanalyze the same data using Bayesian methods that overcome these problems .
We find that the data always favor isotropic models for the distribution of observed polarizations over counterparts that have a cosmological anisotropy of the type advocated in the earlier study .
Although anisotropic models are not completely ruled out , the data put strong lower limits on the length scale \lambda ( in units of the Hubble length ) associated with the anisotropy ; the lower limits of 95 % credible regions for \lambda lie between 0.43 and 0.62 in all anisotropic models we studied , values several times larger than the best-fit value of \lambda \approx 0.1 found in the earlier study .
The length scale is not constrained from above .
The vast majority of sources in the data are at distances closer than 0.4 Hubble lengths ( corresponding to a redshift of \approx 0.8 ) ; the results are thus consistent with there being no significant anisotropy on the length scale probed by these data .