Marginalised posterior distributions of the parameters ${\overline{I}}_{\nu }^2{b}^2$ and ${\overline{I}}_{\nu }^2{\overline{n}}_{\mathrm{eff}}^{-1}$ for the different surveys listed in Table 4. The left and right panels refer to the optimistic and pessimistic cases, respectively. Shown are the 68% and 95% credible regions (shaded) and the underlying true values (dotted). Also indicated is the figure of merit defined in Eq. (42).