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From |
"Nick Cox" <n.j.cox@durham.ac.uk> |

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

Subject |
st: RE: vwidth in old boxplot graphics |

Date |
Tue, 23 Aug 2005 18:52:43 +0100 |

It is still available in Stata as -graph7, box vwidth-. Programming this yourself in Stata 8 or 9 would be possible, I guess, but not quite trivial. In my view, wanting something like this touches on a key limitation of box plots: they often leave out far too much detail. Box plots, I suggest, are optimal when the number of groups concerned is >~ 10 and severe compression is needed to see "the wood for the trees". With fewer groups, more detail is often tolerable and even highly desirable. (Incidentally, an example which I owe to a Howard Wainer paper is instructive. How do you interpret a box plot like this? +---------------+------------------+ +----| | |----+ +---------------+------------------+ Most people I have asked go for a diagnosis of a short-tailed distribution. This forgets that if the half the distribution is inside the box, then the other half must be outside. In this case, the average density in the tails must be much higher than in the centre and the best guess has to be a U-shaped distribution. Boxplots can be much harder to interpret than you think!) Alternatives such as -dotplot- (official), -onewayplot- (user-written), -beamplot- (user-written) dedicated to the idea of showing one symbol for every data point have the advantage that a clear impression of the number of data points is given. Yet further plots are possible showing all the quantiles. -quantile- (official) is here less flexible than -qplot- (user-written). The next issue of the Stata Journal will carry a long diatribe on quantile plots and will be accompanied by an enhanced version of -qplot- (and also of -distplot-, also user-written). A yet further possibility is to hybridise dot and box plots. One example is given by Wild and Seber, "Chance encounters" p.122. Fortuitously, just this afternoon a colleague and I came up with our own hybrid. This assumes a categorical variable coded by successive integers. I wouldn't defend this default design to the limit as it was entirely optimised for one particular dataset. However, the main point is that your own hybrid design is attainable with some coding. (Varying width boxes do sound a bit harder.) For this to work, you need -onewayplot- from SSC. Silly example: . sysuse auto . myboxplot mpg rep78, magic(-0.2) rbar(barw(0.15)) ysc(noreverse) stack h(0.5) *! 1.0.0 NJC/ISE 23 Aug 2005 program myboxplot version 9 syntax varlist(min=2 max=2 numeric) [if] [in] /// [, magic(real 0.4) rbar(str asis) * ] marksample touse qui count if `touse' if r(N) == 0 error 2000 tokenize `varlist' args y cat tempvar median upq loq offset qui { egen `median' = median(`y') if `touse', by(`cat') egen `loq' = pctile(`y') if `touse', by(`cat') p(25) egen `upq' = pctile(`y') if `touse', by(`cat') p(75) gen `offset' = `cat' + `magic' } onewayplot `y' if `touse', by(`cat') msy(+) msize(small) /// plot(rbar `upq' `median' `offset', /// barw(0.25) blcolor(black) bcolor(gs14) hor legend(off) `rbar' /// || rbar `loq' `median' `offset', /// barw(0.25) bcolor(gs14) blcolor(black) hor `rbar') /// xti("`: variable label `y''") ysc(reverse) yla(, noticks) yti("") `options' end Nick n.j.cox@durham.ac.uk > -----Original Message----- > From: owner-statalist@hsphsun2.harvard.edu > [mailto:owner-statalist@hsphsun2.harvard.edu]On Behalf Of skreisel > Sent: 23 August 2005 17:17 > To: statalist@hsphsun2.harvard.edu > Subject: st: vwidth in old boxplot graphics > > > What happend to the usefull Stata 7.0 box-plot command [graph y, box > by(x) vwidth]? Does anyone know of an alternative to graphically > highlight the N of each boxed group by adjusting its relative width? > Regards > Stefan Kreisel > * > * 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/ > * * 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/

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