Figure 3. The polycrystalline estimate of the dielectric constant for the different crystal systems.

The violin outlines are the Gaussian kernel density estimates of the data points that appear in the middle and are calculated using $f(x)=\frac{1}{nh}{\sum }_{i\mathrm{=1}}^{n}K\left(\frac{x-x_i}{h}\right)$ where K is the Gaussian kernel and h is a smoothing parameter (estimated here using Scott's normal reference rule³⁰). The left (blue) refers to the electronic component while the right (yellow), to the ionic. The total number of compounds in each crystal system was: 236, 132, 254, 183, 166, 11 and 74 (for cubic, hexagonal, trigonal, tetragonal, orthogonal, monoclinic and triclinic respectively).