Means Difference Set for Volcano Plots Use this option to specify which set of differences between mean to use for generating the Volcano Plots. Available options are described in the following table: Option Definition All Pairwise Differences Choose this option to examine differences between all possible pairs of levels. Differences with a Control Choose this option to take differences against a single reference level. Note: You must specify the reference control level in the Means Control Value(s) field. None Choose this option to ignore Means differences. To Specify the Means Difference Set: Click the radio button corresponding to the difference set you want to use.