![]() ![]() ![]() Here is a useful plot from wikipedia for better understanding the boxplot by comparing the box plot against the probability density function (theoretical histogram) for a normal N(0,1σ2) distribution. Here is a full discussion about the whisker of boxplot in default R code: In this type of box plot, you can specify the constant k by setting. For a Tukey box plot, the whisker spans from the smallest data to the largest data within the range Q1 - k IQR, Q3 + k IQR where Q1 and Q3 are the first and third quartiles while IQR is the interquartile range (Q3-Q1). A line is drawn across the box at the sample median. The other dimension of the box does not represent anything in particular. The length of the box is thus the interquartile range of the sample. Click Reset (recommended) Select the variable for which you wish to create a boxplot, and move it into the Boxes Represent box. Select Simple and Summaries of separate variables. Click Graphs -> Legacy Dialogs -> Boxplots in earlier versions of SPSS. A value of zero causes the whiskers to extend to the data extremes. Tukey Box Plot is the default box plot in Vega-Lite. The box of the plot is a rectangle which encloses the middle half of the sample, with an end at each quartile. Click Graphs -> Boxplots in SPSS version 29. If range is positive, the whiskers extend to the most extreme data point which is no more than range times the interquartile range from the box. This determines how far the plot whiskers extend out from the box. Here is what’s described in the boxplot() document: Anatomy of a Box and Whisker Plot Instead of displaying the raw data points, a box and whisker plot takes your sample data and presents ranges of values based on quartiles using boxes and lines. The range can be adjusted via argument range in boxplot() function, whose default value is 1.5. Whereas the lower whisker is located at the *larger* of the smallest x value and Q_1 – 1.5 IQR. So the upper whisker is located at the *smaller* of the maximum x value and Q_3 + 1.5 IQR, Lower whisker = max(min(x), Q_1 – 1.5 * IQR) Upper whisker = min(max(x), Q_3 + 1.5 * IQR) But the ends of the whiskers can represent several possible alternative values…”In R’s default boxplot code, “… the bottom and top of the box are always the 25th and 75th percentile (the lower and upper quartiles, respectively), and the band near the middle of the box is always the 50th percentile (the median ). ![]()
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