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RE: st: RE: broken axis symbol?


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   RE: st: RE: broken axis symbol?
Date   Wed, 14 May 2003 21:15:29 +0100

Nick 
n.j.cox@durham.ac.uk 

> -----Original Message-----
> From: owner-statalist@hsphsun2.harvard.edu
> [mailto:owner-statalist@hsphsun2.harvard.edu]On Behalf Of Nick Cox
> Sent: 14 May 2003 19:39
> To: statalist@hsphsun2.harvard.edu
> Subject: RE: st: RE: broken axis symbol?
> 
> 
> Constantine Daskalakis
> > 
> > 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 
> > misleading than 
> > 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 
> your apparent position here.
> 
> 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 
> n.j.cox@durham.ac.uk 
> 
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