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From |
"Wallace, John" <John_Wallace@affymetrix.com> |

To |
"'statalist@hsphsun2.harvard.edu'" <statalist@hsphsun2.harvard.edu> |

Subject |
RE: st: RE: Re: Other Box plots |

Date |
Mon, 2 Dec 2002 10:41:52 -0800 |

In Probability and Statistics (JL Devore, Duxbury Press, MA 1995) the author describes a "Boxplot Rule" for evaluating outliers. Two outlier limits are calculated using the Interquartile range: the first at 1.5 * IQR(measured symmetrically from the 25th and 75th percentiles), and the second at 3*IQR. "Mild" outliers, in this scheme are between the two limits defined above (at either tail). "Extreme" outliers are beyond the 3*IQR limits. Note that this is a different application that just a pictorial summary of the data (which the various plots we've been talking about do), the plot I'm describing allows you to make judgements about how likely it is that suspect points in your dataset are outliers. The whiskers of the plot would span a larger range than the data itself, given a "normal" sample. For that reason, I would want the whiskers out to 3*IQR replaced by the data points themselves. I understand what you're saying about the -box- and -box2- ados; I was uncertain about what the whiskers on the -graph, box- command represented. -JW -----Original Message----- From: Nick Cox [mailto:n.j.cox@durham.ac.uk] Sent: Monday, December 02, 2002 9:32 AM To: statalist@hsphsun2.harvard.edu Subject: RE: st: RE: Re: Other Box plots Wallace, John replied to Fred Wolfe: > > Thanks Fred, thats a huge improvement. The whiskers appear > to behave as > percentiles however (5th & 95th, perhaps?) rather than > functions of the IQR. > Still a useful display though! > I've got lost in this thread in terms of what you want. -box- and -box2- are wrappers for -graph, box by()-. The box plots they produce are exactly those produced by -graph, box-: the only difference is that a preliminary -sort- command is rendered unnecessary (setting aside the fact that the sort order of your data may be changed). Nick n.j.cox@durham.ac.uk * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/ --- Incoming mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.423 / Virus Database: 238 - Release Date: 11/25/2002 --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.423 / Virus Database: 238 - Release Date: 11/25/2002 * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**RE: st: RE: Re: Other Box plots***From:*"Nick Cox" <n.j.cox@durham.ac.uk>

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