Intensities of the 6.9 (top) and 7.25 (bottom) µm bands compared to the 11.2 µm feature intensities normalised to the intensity of the 6.2 µm feature. Filled markers represent sources where both aliphatic bands have been detected, while unfilled markers represent sources where only the 6.9 µm band has been detected. For the 6.9 µm band, the correlation coefficient is 0.84, and improves to 0.92 when only considering sources where both aliphatic bands are detected. For the 7.25 µm band, a weak correlation with a correlation coefficient of 0.60 is found.