[Date Prev][Date Next][Thread Prev][Thread Next][Date index][Thread index]
st: RE: vwidth in old boxplot graphics
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
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
For this to work, you need -onewayplot- from SSC.
. 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
syntax varlist(min=2 max=2 numeric) [if] [in] ///
[, magic(real 0.4) rbar(str asis) * ]
qui count if `touse'
if r(N) == 0 error 2000
args y cat
tempvar median upq loq offset
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'
> -----Original Message-----
> From: firstname.lastname@example.org
> [mailto:email@example.com]On Behalf Of skreisel
> Sent: 23 August 2005 17:17
> To: firstname.lastname@example.org
> 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?
> 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: