Box Plot

Updated 01 Oct 2026

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What it is
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  a diagram summarizing a data set's distribution using five key values: minimum, Q1, median (Q2), Q3, and maximum
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Construction
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  the box spans $Q_1$ to $Q_3$ , with a line at the median
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  some versions extend whiskers to the minimum and maximum
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  a common fenced version extends them to the most extreme observations within $Q_1-1.5IQR$ and $Q_3+1.5IQR$ , where $IQR=Q_3-Q_1$
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  observations outside the fences are plotted separately.
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Caution
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  specify the whisker convention and quartile calculation method
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  flagged observations are potential outliers, not automatically data errors
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Source correction
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  the slides' "Block Plot" refers to a box plot
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Interpretation
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  check the whisker convention: some plots use minimum/maximum; others use the most extreme observations within $1.5,IQR$ fences.
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  points beyond these fences are potential Unavailable references, not automaticallly erroneous observations
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Related
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  Quartiles
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  Stem-and-Leaf Diagram

Linked references 3