Scrawl Strips, and Letter or B-Letter Strips: Depicting Marginals of ScatterPlots

摘要

Data from a bivariate distribution is often graphically presented by using ascatter plot. Adding a suitable depiction of the marginal data distributions to the edges of the scatter plot allows interesting features of the marginal data distributions to be seen alongside the original bivariate data. We propose providing these marginal depictions by a modification of Quantile-Quantile plots (QQ plots) we call scrawl strips. We also propose adding a strip or axis showing location of the letter values, or the broadened letter values, which we call a letter strip, or b-letter strip, respectively. These two strips can be combined. Since scrawl strips are modified QQ plots, they inherit useful features of QQ plots. These features include information about the shape of the marginal distribution, the presence and type of skewness, the presence of heavy tails, gaps and ties in the ordered data, appearances of bimodality or high shoulders, and assumptions of normality. This type of information is often either absent or depicted poorly, both in univariate competitors to the QQ plot and in the basic scatter plot.