DÄ internationalArchive7/2010Non-uniform Box Plot
LNSLNS In the article of Spriestersbach et al. (4), it was stated that, in contrast to the box, the definition of the so-called “whiskers” in the box plot diagram is not uniform.

A diagram designated as a “box and whiskers plot” was first described by Tukey in 1977 (1). In this plot, the whiskers extended to the greatest or to the smallest values within a limit, the so-called “inner fence”.

The width of the “inner fence” is defined as one and a half times the interquartile distance. An additional “outer fence” extends to three times the interquartile distance. Measured values outside these limits may be outliers and are designated with special symbols.

A similar diagram had already been described in 1952 by Spear and designated as a “range bar” (2). This diagram corresponds to the description in the text.

On the other hand, Altman set the ends of the whiskers at the 2.5% and 97.5% quantiles (3). The box plot provided by statistics programs is likewise non-uniform. Whereas SAS presents the range bar as standard and only provides the original box and whiskers plot as an option, many other programs (S Plus, R, SPSS, Mathematica) use Tukey’s algorithm as standard.
DOI: 10.3238/arztebl.2010.0122a

Prof. Dr. med. Aiman Obed, FACS, FEBS
Dr. med. Armin Goralczyk
Universitätsmedizin Göttingen
Georg-August-Universität
Abteilung Allgemein- und Viszeralchirurgie
Robert-Koch-Str. 40
37075 Göttingen, Germany
Letters: 37099 Göttingen
agoralczyk@med.uni-goettingen.de
1.
Feinstein AR: Principles of Medical Statistics. Boca Raton, London, New York, Washington D. C.: Chapman & Hall/CRC 2002; 68.
2.
Spear ME: Charting Statistics. New York, London: McGraw-Hill 1952.
3.
Altman DG: Practical Statistics for Medical Research. Boca Raton, London, New York, Washington D. C.: Chapman & Hall/CRC 1st Edition 1991; 33.
4.
Spriestersbach A, Röhrig B, du Prel JB, Gerhold-Ay A, Blettner M: Descriptive statistics: The specification of statistical measures and their presentation in tables and graphs—Part 7 of a series on evaluation of scientific publications [Deskriptive Statistik: Angabe statistischer Maßzahlen und ihre Darstellung in Tabellen und Grafiken – Teil 7 der Serie Biometrie]. Dtsch Artzebl Int 2009; 106(36): 578–83. VOLLTEXT
1. Feinstein AR: Principles of Medical Statistics. Boca Raton, London, New York, Washington D. C.: Chapman & Hall/CRC 2002; 68.
2. Spear ME: Charting Statistics. New York, London: McGraw-Hill 1952.
3. Altman DG: Practical Statistics for Medical Research. Boca Raton, London, New York, Washington D. C.: Chapman & Hall/CRC 1st Edition 1991; 33.
4. Spriestersbach A, Röhrig B, du Prel JB, Gerhold-Ay A, Blettner M: Descriptive statistics: The specification of statistical measures and their presentation in tables and graphs—Part 7 of a series on evaluation of scientific publications [Deskriptive Statistik: Angabe statistischer Maßzahlen und ihre Darstellung in Tabellen und Grafiken – Teil 7 der Serie Biometrie]. Dtsch Artzebl Int 2009; 106(36): 578–83. VOLLTEXT