Upper row: probability density estimation using binning. In the left and right panels, the bin width is the same but the centre of the bin is shifted. Bottom row: density estimation using kernel smoothing. In the bottom left panel the simplest box kernel is used, in the bottom right panel the B₃ spline kernel is used. The kernel shape and size is shown in the upper-right corner of the figures. The rug plot on the bottom axis shows the data points that were used for density estimation.