Dotplots

A dotplot is a graphical display of the distribution of a numeric variable in which each observation is represented by a dot. The dots are placed along a horizontal number line at positions corresponding to the data values, and when several observations share the same value, multiple dots are stacked at that value.

Construction and variants: A standard one-dimensional dotplot uses a single row of dots. Variants include back-to-back dotplots for comparing two groups, side-by-side dot plots, and vertical or rotated dot plots. Dots can be stacked or offset to indicate frequency, and jittering may be used to reduce overplotting at the cost of exact values.

Uses and interpretation: Dotplots help reveal distributional features such as symmetry, skewness, gaps, clusters, and potential outliers. They provide a direct view of each observation, which makes them useful for small to moderate data sets and for teaching concepts of distribution, central tendency, and spread. For larger data sets, histograms, box plots, or violin plots may be more readable.

Limitations and considerations: Overplotting can obscure frequencies when many observations share values, and readability depends on scale and value granularity. Dotplots are less efficient for very large or highly continuous data, where binning or summary plots may be preferable.

See also: histogram, stem-and-leaf plot, box plot, violin plot, back-to-back plot.