Box plot (or box-and-whisker plot) showing the distributions of the derived molecular fractional abundances. The boxes are arranged in ascending order according to the median value. The height of the box represents the interquartile range IQR ≡ [Q₁, Q₃] (i.e. from the 25th to 75th percentile). A horizontal line that goes through the box shows the median abundance (Q₂ or the 50th percentile). The whiskers are defined to extend from Q₁ − 1.5 ×IQR to Q₃ +1.5 ×IQR unless the minimum and maximum values of the distribution are encountered before that (in which case the whiskers extend to the minimum and maximum values). We note that only the uncensored data are used to plot the distributions (i.e. the upper limits are ignored), and SiO was detected in only one of the target sources (SMM 3).