At 02:21 PM 8/28/01 +0000, NoSpam54 wrote:
> If there were an AP stats course, they would probably be using a
>college-level text that would be using a true Tukey boxplot, not the
>Harcourt-Brace/NCTS boxplot. I don't think it fair for students to know that
>the NCTS and the K-12 textbook writers (and the MCAS test writers) have
>adopted
>one feature of the Tukey boxplot, but not the most important feature: the
>ability to flag outliers.
>Eugene Gallagher
however ... the "flagging" of "outliers" is totally arbitrary ... i see no
rationale for saying that if a data point is 1.5 IQRs away from some point
... that there is something significant about that
there may be ... there may not be
just as ANY value in the entire data set could be flawed ...
one could have selected 1.75 IQRs or 1.25 IQRs or some function of a
standard deviation ... or any other value
so, whether we think that the tukey rule for indication is good or not ...
it really boils down to if there should be ANY indication of values ...
ie, highlighted to the boxplot observer ... that are extreme by any
definition ... or not
overall, perhaps that is a good idea ... but, as long as the boxplot user
clearly knows that this does NOT mean 'significant' or 'important' or some
other verbiage that implies that outliers are BAD deviants in some sense of
the word
as for the item #39 on the MCAS test ... i really don't care much if the
boxplot is technically drawn correctly or not ... again, THE important
matter is that the "thing" being assessed by the item is
essentially irrelevant to general statistical knowledge, especially at the
level of a 10th grade student who is learning something about statistics in
the context of their mathematics work ... and again, there is the matter
that the item itself is very poorly constructed ...
>=================================================================
>Instructions for joining and leaving this list and remarks about
>the problem of INAPPROPRIATE MESSAGES are available at
> http://jse.stat.ncsu.edu/
>=================================================================
_________________________________________________________
dennis roberts, educational psychology, penn state university
208 cedar, AC 8148632401, mailto:[EMAIL PROTECTED]
http://roberts.ed.psu.edu/users/droberts/drober~1.htm
=================================================================
Instructions for joining and leaving this list and remarks about
the problem of INAPPROPRIATE MESSAGES are available at
http://jse.stat.ncsu.edu/
=================================================================
