Mixing ratios of CH₃OH ice to the shoulder component of CO₂ ice. Circles and arrows in the top panels indicate measurements and 3σ upper limits, respectively, for the red CMZ objects in this study (left) and for YSOs in the Galactic disc (Pontoppidan et al. 2008, right). In the bottom two panels, probability density functions of the mixing ratio N(solidCH₃OH)/N(CO₂ shoulder) are shown for the CMZ and disc YSOs, respectively. Thin lines correspond to individual measurements, assuming a bivariate normal distribution for the measured column densities and their 1sgr; uncertainties; the thick line shows the sum of all distributions.