Thursday, September 15, 2005
Boxplots in Excel
Boxplots in Excel: "Boxplots in Excel
by Neville Hunt, Coventry University
Acknowledgements
An earlier version of this article was published in The Spreadsheet User Volume 3, Number 2, November 1996.
I am grateful to Rodney Carr for greatly simplifying my original method.
Introduction
A boxplot, or box and whisker diagram, provides a simple graphical summary of a set of data. It shows a measure of central location (the median), two measures of dispersion (the range and inter-quartile range), the skewness (from the orientation of the median relative to the quartiles) and potential outliers (marked individually). Boxplots are especially useful when comparing two or more sets of data. Regrettably, there is currently no boxplot facility in Microsoft Excel. For simplicity, many recent statistics textbooks (for example, Daly et al, 1995) omit the fences used to identify possible outliers. These simplified boxplots, displaying most of the important features, can be drawn quite easily in Excel. In the absence of any fences (see Devore and Peck (1990) for a definition), a simple rule is that a whisker which is longer than three times the length of the box probably indicates an outlier."
by Neville Hunt, Coventry University
Acknowledgements
An earlier version of this article was published in The Spreadsheet User Volume 3, Number 2, November 1996.
I am grateful to Rodney Carr for greatly simplifying my original method.
Introduction
A boxplot, or box and whisker diagram, provides a simple graphical summary of a set of data. It shows a measure of central location (the median), two measures of dispersion (the range and inter-quartile range), the skewness (from the orientation of the median relative to the quartiles) and potential outliers (marked individually). Boxplots are especially useful when comparing two or more sets of data. Regrettably, there is currently no boxplot facility in Microsoft Excel. For simplicity, many recent statistics textbooks (for example, Daly et al, 1995) omit the fences used to identify possible outliers. These simplified boxplots, displaying most of the important features, can be drawn quite easily in Excel. In the absence of any fences (see Devore and Peck (1990) for a definition), a simple rule is that a whisker which is longer than three times the length of the box probably indicates an outlier."
