R-beta: CI for median in funtion boxplot

(Ted Harding) Ted.Harding at nessie.mcc.ac.uk
Mon Apr 6 15:14:45 CEST 1998

On 06-Apr-98 Bill Venables wrote:
> But why do people still look at boxplots so much, and why do they
> spend so much time and technology on them?  It really puzzles me.
> With all the good work done in recent years on bandwidth
> selection, why don't we communicate this kind of information,
> between ourselves at least, with kernel density estimates more?
> They could be embellished with a few reference percentiles, of
> course, but to me they convey a whole lot more than boxplots.  It
> can't be very long before, like pie charts, boxplots are reserved
> for politicians, advertising agents and others of their kind.
>  > I don't know the exact history; in any case, John Tukey
>  > devised the boxplot, including the notches, and ``1.58 is THE
>  > number''.

Like many early Tukey schemes, the boxplot was devised in days when most people
only had line-printer output readily available. If you think about it, the
boxplot can be drawn (to within character-width resolution) using basic ASCII
symbols like - + | on a lineprinter/dumb terminal. "Experimental Data Analysis
was written in 1976! The same is true for stem-and-leaf diagrams and the like.
And very effective, too, for that medium.

Tukey's graphical tricks were, for many people, the first experience they had
of the comprehensible display of statistical summary data and I remember the
furious eagerness with which they were accepted in groups whom more academic
statisticians had previously regarded as, for practical purposes, out of reach;
and tribute must be paid to pioneering teachers like the late Cathie Marsh who
saw these methods as the bridge by which true understanding of data could be
brought to them.

As to why people still look at them, well, <cynical>old habits die hard, and
something which works to your satisfaction is a better ploy than adapting to
something new which may require unknown effort which you are not sure might be
well spent</cynical>, but Bill's point, essentially that modern display
technology can greatly improve on this without stressing the learner, seems
good. (I still wonder a bit, though, whether someone used to a boxplot would
readily derive the same information from a kernel density estimate without
considerable practice).

Best wishes to all,

E-Mail: (Ted Harding) <Ted.Harding at nessie.mcc.ac.uk>
Date: 06-Apr-98                                       Time: 14:14:45
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