RE: st: RE: broken axis symbol?

 From "Nick Cox" <[email protected]> To <[email protected]> Subject RE: st: RE: broken axis symbol? Date Wed, 14 May 2003 21:15:29 +0100

```Nick
[email protected]

> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]]On Behalf Of Nick Cox
> Sent: 14 May 2003 19:39
> To: [email protected]
> Subject: RE: st: RE: broken axis symbol?
>
>
> >
> > At 01:04 PM 5/14/03, Nick Cox wrote:
> > >As I recall, Darrell Huff in his 1954 book implied that axes
> > >which don't start at zero are deceitful. And I seem
> > >to remember my high-school science teachers saying the
> > >same thing in the 1960s and recommending a scale break.
> > >[snip]
> > >
> >
> > I beg to differ on this one Nick.
> > I think being able to "break" the axis is a crucial feature
> > in plots.
> >
> > Suppose I want to plot the percent of adolescents who've
> > ever used a
> > computer in the US over the past 10 years (estimated from
> repeated
> > cross-sectional samples). During that period, this
> > proportion has gone up
> > from about 70% or so to over 95%.
> >
> > Y-axis is "% used computer" and X-axis is calendar time (years).
> >
> > First, I don't want to plot on the log scale. Why would I?
> >
> > Second, I don't want to waste three quarters of my graph
> > area by using the
> > full scale of the Y axis (i.e., 0-100%), when all my
> > measurements are
> > around 85-95%.
> >
> > I can start my Y-axis at, say, 60%, but I think that's more
> > starting at 0% and having a "break" to jump to, say, 60%.
>
> Your example doesn't convince me, but I think there
> are better ones. In principle, I agree with this:
> there is sometimes a need for scale breaks.
>
> Evidently I should make my position clearer.
>
> Ernest asked for a scale break indicated
> in a particular way by a zig-zag on the axis.
>
> My assertion is that not using that is not bad
> practice, contrary to some old advice, and to
>
> My question is how far it is really used in
> scientific literature(s).
>
> In addition, I drew attention to Cleveland's
> suggestion for a full scale break whenever
> a scale break is deemed essential.
> Graphically this is a very different
> practice. It is a matter of dividing the
> data region into different panels.
>
> In fact, one objection to the zaggy
> axis is that it is not nearly drastic
> enough as a way of signalling something
> fundamental about the graph. Users too naive
> or lazy to look at labels are also likely
> to overlook the zags (or perhaps the zigs).
>
> In my previous posting
> I referred to an FAQ I wrote giving
> a real example and explaining one way to
> do it in Stata <8, at least roughly,
> and as said the principle could be
> applied with Stata 8.
>
> What would do you do with a graph showing
> SARS cases against time? Time starts
> late 2002, say.
>
> Nick
> [email protected]
>
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```