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Re: st: Box and whiskers graph


From   Marcello Pagano <[email protected]>
To   [email protected]
Subject   Re: st: Box and whiskers graph
Date   Tue, 06 Jul 2004 13:21:58 -0400

Oops, that should read 99.2%, not 99.7% .

m.p.

Marcello Pagano wrote:

What Ted said is quite correct, but you can also exercise your imagination and notice that if you have normal data, then the expected value of the interquartile range is 1.34 sigma (just reading from the normal tables). Thus, in this case, the adjacent values are estimates of mean plus or minus twice the interquartile range, or mean plus or minus 2.64 sigma. That means that you should have almost all your data (99.7%) between the two adjacent values.

m.p.

S�ren O'Neill wrote:


Thank you very much for your reply - is there a reference you can give me, that explains the reasoning behind these adjacent values - personally I rely mostly on the book Practical Statistics for Medical Research by D. Altman and I cant seem to find any reference to 'adjacent values' therein ... Also the Stata Users guide and reference manuals seem to come up short ...

Kind regards
Soren

On Monday 05 July 2004 23:32, Ted Anagnoson wrote:


The adjacent values separate the outliers from the rest of the data. They
are the 25th or 75th percentiles plus 1.5 times the Inter-Quartlile range,
which is the distance between the 25th and 75th percentiles. However, the
adjacent value indicated on the graph, by convention, is "rolled back" to
an actual data point, so that there is always real data underneath the
adjacent value.

So the adjacent values are not actually percentiles....but "adjust" to the
characteristics of the data.

Ted Anagnoson
California State University Los Angeles

At 10:46 PM 7/5/04 +0200, you wrote:


The box and whiskers graph illustrates the median value (with a line), the
25%
and 75% centiles (with a box) and the adjacent values (with the whiskers)
... but what are the adjacent values? 2� and 97� centiles or ... ???
--
S�ren O'Neill, kiropraktor
[email protected]
tel. 6362 1906


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______________________________________________________________________

Marcello Pagano
Biostatistics Department               Tel: 1-617-432-4911
Harvard School of Public Health        Fax: 1-617-739-1781
655 Huntington Avenue                  email:[email protected]
Boston, MA  02115                      http://biosun1.harvard.edu/~bio200
USA

eppur si muove


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