Cleveland Dot Plots

A Cleveland dot plot looks like a bivariate plot, and is sometimes used as such, but in its typical usage it is better considered (in my opinion) as a univariate plot where the different data values, represented by dots, carry identifying labels, even though the data values may be summary statistics such as the mean or percentiles (see Jacoby 2006). A very different type of dot plot is shown in the next entry. R-wise it comes down to this: Cleveland dot plots are what you get with dotchart (or its lattice companion "dotplot"), whereas the other type of dot plot is created by ggplot2 with geom_dotplot.

The terminology concerning dot plots or dot charts is not firmly established, occasional claims to the contrary notwithstanding. Both the plots described in this entry as well those created by dotplot, plus sometimes others, can be found under the headings of "dot plots" or "dot charts". However, the term "Cleveland dot plot" (after statistician and data visualisation expert William S. Cleveland [1983]) has been coined to highlight this particular type of chart, and I follow this usage. The Stata User's Guide does not use this term and it conceives of graph dot as a device for the display of summary statistics such as means or percentages.

Command dotchart

The plot below, showing the percentage of women aged 25 to 49 in paid work (OECD data from 2007, see Ludwig-Mayerhofer et al. 2014, p. 51), was created as follows:

dotchart(sort(do4$lfp07_age2549),
pch = 19,              # plot character 19
pt.cex = 1.1,          # slightly increases size of plot elements
labels = do4$country[order(do4$lfp07_age2549)],
frame.plot = FALSE),   # Removes frame

Cleveland dot plot

Note sort that precedes the reference to variable "lfp07_age2549" in data object "do4"; otherwise, the data would appear in the order in which they are found in the data set. Likewise, [order(do4$lfp07_age2549)] informs R to display the labels, taken from variable "country", in the same order as the data values.

Lattice version

The lattice package contains procedure dotplot, which may be outlined in more detail at a later stage.

References

Cleveland, William S. (1983): Visualizing Data, Hobart Press.
Jacoby, William G. (2006): The Dot Plot: A Graphical Display for Labeled Quantitative Values, The Political Methodologist. Newsletter of the Political Methodology Section, American Political Science Association, Vol. 14, Number 1, pp. 6-14.
Ludwig-Mayerhofer, Wolfgang/Liebeskind, Uta/Geißler, Ferdinand (2014): Statistik. Eine Einführung für Sozialwissenschaftler, Weinheim, Basel: Beltz Juventa.