The smoothness factor of the Lowess Curve Line. It must be between 0 - 1. The default value is set to 0.25.
It is the portion of points used in finding the n nearest points. In other words, n = smoothness * no_of_points. A larger value will result in a smoother curve. A smaller value will result in the curve tracking the data points better.
For the Lowess Curve Line to have any smoothing effect at all, n must be at least 3. You may need to use a large smoothness factor if you only have a few data points.