Histograms showing the effect of contamination correction on the 850–450 μm average flux ratio 〈S₈₅₀〉〈S₄₅₀〉⁻¹. The number of sources for each bin is given before (black bars) and after (grey bars) contamination correction is applied to the measured ratio. The histogram bins have a width of 0.02, with a range going from 0.00 to 0.26. Top: the histogram is limited to the 33 sources chosen in this study for their high level of molecular contamination. Bottom: the histogram including all 60 sources shown in Fig. 5.