Dennis Roberts wrote:
>
>At 12:31 PM 8/27/01 +0000, EugeneGall wrote:
>> The Harcourt-Brace description of the boxplot, which is now being taught
>>to MA students, isn't a proper boxplot (maybe the Harcourt-Brace K-12
>boxplot
>>is different from the Tukey boxplot), becuase it doesn't properly plot
>>outliers
>>and extreme outliers.
>
>
>of course, boxplots do NOT have to show outliers if there are none,
>correct? so, what you are saying is that in THIS case ... since you have
>done more digging into the boxplot put on item 39 ... and have concluded
>that it is not properly designated ... that it is wrong
>
>now, i made a data set ... here is the old time boxplot ... that you can
>get from minitab ... which is perfectly legit ...
>
>Boxplot
>
>
> ---------------------
> --------------------I + I----------
> ---------------------
> ----+---------+---------+---------+---------+---------+--C1
> 20.0 22.0 24.0 26.0 28.0 30.0
>
>there is no designation for outliers since, by definition in this data set
>... there are none
>
>in the better graphic version minitab has ... all you see are single lines
>extending from the hinges ... with NO other symbols (dots, etc.)
>
>thus, in the item 39 example ... while i assume that the dots at both ends
>are just meant to show where the data stop ... this is not how (i dare
>say?) ANY software would show it ...
>
>however, if the boxplot were done by hand ... you might see the texts that
>they are using depict it this way ... draw a box ... extend lines ... put
>dots at the end to signify more clearly ... the ends ... and the notion of
>"outliers" MAY NOT enter into the discussions carried on in mass. class
>curricula ...
>
>in any case ... we have a messy item ... by ANY criterion used
The MA curriculum guidelines uses a boxplot figure from the Harcourt Brace
glossary. An interactive version of the MA curriculum guidelines with a link to
the boxplot def is posted at:
http://www.doe.mass.edu/frameworks/math00/
This definition of boxplot where the whisker extends to cover ALL the data
follows the definition of boxplot at the National Council for Teaching
Mathematics.
http://standards.nctm.org/document/index.htm
This NCTM boxplot is NOT the boxplot that Tukey described and it is not the
boxplot that you get with SPSS, SAS, Minitab or Matlab (the packages that I
have at hand). The two boxplots are the same if there are no outliers. BUT,
the virtue of the Tukey boxplot is that it allows you to see the outliers.
I have no idea why the NCTM decided to create a different boxplot. I don't
have the original Tukey paper, but I do have Cleveland's books, Tufte's books
and a number of other books describing the boxplot. None follow the NCTM
method of drawing a boxplot.
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