The Densities options provide several ways to compare the distribution and composition of the response across the levels of the X factor. There are three density options:
Compare Densities shows a smooth curve estimating the density of each group. The smooth curve is the density estimate for each group.
Composition of Densities shows the summed densities, weighted by each group’s counts. At each X value, the Composition of Densities plot shows how each group contributes to the total.
Proportion of Densities shows the contribution of the group as a proportion of the total at each X level.
Related Information 

Help created on 9/19/2017