Re: st: RE: Error Bars on Histogram or Bar Plots

[Buzz Burhans <wsb2@cornell.edu>]

> > How do you put error bars on histograms or bar plots? I am
> > using Stata 8 in Windows.
>
> I don't think either is supported as a standard option.
I believe these were the posts that generated a great deal of consideration 
over the last week regarding sliding bins  for histograms, histograms vs 
bar graphs, and  the role of visual data exploration.

Having just spent a fair bit of time plotting some data for publication 
this weekend, I'd like to return to the original question regarding error 
bars. I have been using Stata 8, and I like the graphics.  It seems though, 
that there is something fundamentally wrong with a statistics graphing 
program that doesn't facilitate the use of error bars on plots, whether 
connected  line plots or bar graphs.  Error or uncertainty is a major 
element of what we often wish or need to represent in a graphical 
representation of data.  Stata makes one cob up solutions for this when it 
should be facilitating them. Yes, one can get it done, but not always 
easily or correctly for that matter.  For instance,overlaying a range plot 
works, but I don't think one should have to have a marker on both ends of 
the "error bar", and I don't think that if the plotting symbols of the data 
are open symbols, the error bar should more than touch the edge...in fact 
there are journals that specifiy that there should not be markers in markers.

One of the best implementations of error bars in Stata has been Paul Seed's 
XTGRAPH; it is a nice implementation for a number of reasons: 1)It is built 
in to the process of plotting the data; 2) it allows a great deal of 
flexibility in the selection of the type of error one wants to represent; 
3) It facilitates picking up and plotting the error terms from a previously 
run model 4) it facilitates visual issues by allowing half error bars or 
offsetting the plotted points.

It has some challanges for those of us who want to use it without hacking 
the code...it is not easy to control the symbol types, and the error bars 
come inside open symbols with their marker ends, but it is a really nice 
tool.

In any case, it is a nice example of a set of features that I think Stata 
should be more concerned about implementing.  The issue of error terms 
seems fundamentally a part of what statisitics is about, and to have a 
powerful graphics package that essentially ignores the need to represent 
that element ( I recognize there is some implemention made vis a vis the CI 
plots).  In the journals I read, error bars are commonly used, and it seems 
to me implementation of adding them to graphs easily and flexibly is an 
important feature that Stata Corp. should address.  It should be as easy to 
add error bars to bar graphs, as the original post requested, and to other 
graph types as well (twoway connect for example)

Buzz Burhans

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