Comparison of the reference and estimated N-PDFs when inverting the N-PDF on the spatially and spectrally averaged ORION-B data. The thick red line indicates the N-PDF as a histogram constructed directly from the dust-derived Orion B column densities, and the green line represents a χ² fit to the red histogram. The estimated N-PDFs from the 10 000 MCMC iterations to sample the Bayesian posterior are shown with blue circles. The dashed orange line is the MAP estimation for the N-PDF. The vertical dotted black line indicates the limit below which the line intensities predicted by the emission function fall below the typical noise level of the data, that is, 0.1 K km s⁻¹.