Integrated intensity for 84 GHz (left) and 95 GHz (right) masers, with and without SiO (2−1) wings. In each box plot the horizontal coloured line represents the median value, the box represents the interquartile range between the 25th and 75th percentiles, and the vertical lines (the ‘whiskers’) show the ranges from the minimum value to the 25th percentile and from the 75th percentile to the maximum value.