our 3 or 5 parameter models, the simulated PS will be different from the true one due to the numerical implementation. We assume for this a constant multiplicative error of 25 per cent, guided by the observed 10–30 per cent difference at the relevant scales between [<span style="font-variant:small-caps;">21CMFAST</span>]{} and the cosmological RT simulations in @Zahn:2011p1171. For each mock observation of the 21 cm PS, we add this 25 per cent error in quadrature with the noise contribution from equation (\[eq:T+S\]). In principle this would be a correlated error, however, at this stage a constant multiplicative factor is sufficient. Below, we include some results excluding this error, showing the maximum information which can be extracted from the signal assuming a perfect characterization of modelling uncertainties.

To sample the reionization parameter space in [<span style="font-variant:small-caps;">21CMMC</span>]{}, we perform a smaller, lower resolution [EoR]{} simulation. Using a different set of initial conditions to the mock observations, we simulate a 250$^{3}$ cMpc$^{3}$ volume with an initial grid of 768$^{3}$ voxels smoothed down on to a 128$^{3}$ grid. Our two simulations are both sampled at the same physical resolution ($\sim2$ Mpc), and resampled by the same factor of 6 from the initial density grid to ensure 