A quantile/box plot is a combination of two basic univariate plot types. The quantile plot shows the distribution of measurements while the companion box plot shows a statistical summary of that distribution. (See the other samples for detailed descriptions of the quantile and box plot types.) This combination provides a thorough perspective of a particular measure.
The following is a plot of the petal lengths of all irises in a particular study.
Here it can be seen that the petal lengths do not form the standard sigmoid pattern which is to be expected for normal distributions. In fact, there appear to be two distinct and separate sigmoids in the plot, a small one in the lower left and a larger one in the upper right. This suggests that there may be more than one type of sample in the study. Of course, this turns out to be true in that the study encompassed three different species of iris. (It can be discovered through further exploration that the Setosa records are those in the lower left while the Virginica and Versicolor records are those in the upper right.)
The data presented here is from E. Anderson's study of 3 species of iris, The Irises of the Gaspe Peninsula, which was published in 1935 in the Bulletin of the American Iris Society.
This data (and visual) is supplied with VisiCube as a sample project.
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