# Naming Convention for distribution plots

I have come across a picture of a density plot that I understand visually and conceptually but I am confused by the terminology. It is referred to as simply a "Density Plot". Have a look:

Question: If a researcher refers to a graph as a density plot, what does he/she probably mean?

Unfortunately I couldn't find the URL to accompany the picture, so we won't be able to examine everything under the hood. However, I'm hoping someone can tell what it most likely is just by glancing at it, or at least weigh in on what the conventional understanding of "Density Plot" implies.

If I'm not mistaken there are many types of densities plots. If I had to guess, judging by the smoothness, it is a kernel distribution of some sort. I did a bit of research and found out there are many types of kernel distributions: Epanechnikov, uniform, triangular, biweight, normal, and cosinus just to name a few.

Since there are so many out there, I'm wondering if we wouldn't have to specify which type of density is being plotted? Or is one type much more common than the other types, to the effect that "Density Plot" is assumed to mean that type and not any other type unless otherwise stated?

• I better see what you mean now. Ideally, you would have this information with the graph. This is a biased view, but in my field, most people do not put this information with density graphs. Usually you can find it in the methods section. If this is missing, I try to guess what was done by how the graph looks. Here, this graphs looks like it came from ggplot which is an R package, so I would guess this was generated using the density() function with default parameters. But I cannot be certain, of course. – Daniel Feb 10 '18 at 19:09
• Ok cool, that helps. I don't know too much about R, but just out of curiosity, what is the default setting for density estimation method for R's density() ? Like you said, we can't be certain, but perhaps R's default setting here and my search for the conventional terminology are one and the same. – Arash Howaida Feb 10 '18 at 19:41
• You can find more details here: stat.ethz.ch/R-manual/R-devel/library/stats/html/density.html. But by default, density() uses a Gaussian kernel. – Daniel Feb 10 '18 at 19:46