The Double-Y histogram can be considered to be a combination of two separately scaled multiple histograms. Two different series of variables can be selected. A frequency distribution for each of the selected variables will be plotted but the frequencies of the variables entered into the first list (called Left-Y variables) will be plotted against the left-Y axis, whereas the frequencies of the variables entered into the second list (called Right-Y variables) will be plotted against the right-Y axis. The names of all variables from the two lists will be included in the legend followed by a letter L or R, denoting the Left-Y and Right-Y axis, respectively. This graph is useful to compare distributions of variables with different frequencies.

See also, 2D Histograms and Graphs - 2D Histograms.