A box plot shows the five-number summary of the data – the minimum, first quartile, median, third quartile, and maximum. An outlier box plot is a variation of the skeletal box plot that also identifies possible outliers.
An outlier box plot is a variation of the skeletal box plot, but instead of extending to the minimum and maximum, the whiskers extend to the furthest observation within 1.5 x IQR from the quartiles. Possible near outliers (orange plus symbol) are identified as observations further than 1.5 x IQR from the quartiles, and possible far outliers (red asterisk symbol) as observations further than 3.0 x IQR from the quartiles. You should investigate each possible outlier before deciding whether to
exclude it, as even in normally distributed data, an outlier box plot identifies approximately 0.7% of observations as possible outliers.
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