> : Nick Cox [mailto:[email protected]]
> It's not the answer you want, but I really don't understand
> why these pyramids are so popular, or even why their key
> limitation is not mentioned more frequently. It must be
> some sort of social feedback loop, as with pie charts, that
> within certain groups pyramids are familiar, therefore expected,
> and vice versa.
[...]
> A pyramid obliges the reader mentally to pick up one bar and lay it down
> on top of its neighbour. I don't believe that many of us are
> very efficient at doing that in our heads.
I agree that this is a real disadvantage of population pyramids. There is a
workaround for this by mirroring the shape on the vertical axis with a
stacked bar on the minor side showing the difference to the other side. But
this is no perfect solution. Population Pyramids are better in showing big
differences or time trends: My former students always loved this page:
http://www.census.gov/ipc/www/idbpyr.html (Choose a interesting country,
click "dynamic" and "Submit query").
In my case the situation looks like a pop-pyramid but is not: The top left
bar would probably show Prostate cancer for men, and the top right bar
breast cancer for women as the most frequent sex-specific cancer
localisations (I mixed up the sides in my first mail). The second bar from
the top would show the second most frequent localisations for men and women
and so on. So comparison of left and right bar is not the major point here.
In my experience it's a quite useful basic graph for cancer data because
many people are interested in cancer ranks. With this graph it's easy to see
and to compare between the sexes. Plus one gets information on frequencies,
too.
Best wishes
Stefan
*
* 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/
