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We review, compare and extend recent studies searching for evidence for apreferred cosmological axis. We start from the Union2 SnIa dataset and use thehemisphere comparison method to search for a preferred axis in the data. Wefind that the hemisphere of maximum accelerating expansion rate is in thedirection $(l,b)=({309^\circ}^{+23^\circ}_{-3^\circ},{18^\circ}^{+11^\circ}_{-10^\circ})$ ($\omm=0.19$) while the hemisphere ofminimum acceleration is in the opposite direction$(l,b)=({129^\circ}^{+23^\circ}_{-3^\circ},{-18^\circ}^{+10^\circ}_{-11^\circ})$($\omm=0.30$). The level of anisotropy is described by the normalizeddifference of the best fit values of $\omm$ between the two hemispheres in thecontext of \lcdm fits. We find a maximum anisotropy level in the Union2 data of$\frac{\Delta \ommax}{\bomm}=0.43\pm 0.06$. Such a level does not necessarilycorrespond to statistically significant anisotropy because it is reproduced byabout $30%$ of simulated isotropic data mimicking the best fit Union2 dataset.However, when combined with the axes directions of other cosmologicalobservations (bulk velocity flow axis, three axes of CMB low multipole momentsand quasar optical polarization alignment axis), the statistical evidence for acosmological anisotropy increases dramatically. We estimate the probabilitythat the above independent six axes directions would be so close in the sky tobe less than $1%$. Thus either the relative coincidence of these six axes is avery large statistical fluctuation or there is an underlying physical orsystematic reason that leads to their correlation.

Searching for a Cosmological Preferred Axis: Union2 Data Analysis and Comparison with Other Probes