Probability density of the Bayes factor, lnR₀₁, shifted to have its true value at 0. The black curve is the distribution of ΔlnR₀₁ extracted from the full nested sampling analysis, and the blue curve is the distribution extracted from the approximation from Sect. 3. The green curve corresponds to the highly discrepant case of one of four tomographic redshift bins being shifted by dz = 0.3. Dotted lines mark the mean of each distribution.