st: Before and After Pairwise Plots

[C Rose <junk7@microserf.org.uk>]

Dear all

I'm very new to Stata, so please excuse me if this has been answered  
before.

I'd like to know how to produce a plot that shows how a dependent  
variable, measured for a number of individuals, changes after an  
intervention. I have managed to find an FAQ on the topic for older  
versions of Stata, which explains the situation quite clearly (please  
see http://www.stata.com/support/faqs/graphics/vplplot.html), as does  
the referenced paper. I'm using Stata/IC v10.

It seems the "twoway pcspike" command is appropriate, but I have two  
questions about this:

1. This requires one to have data in the form y1 x1 y2 x2. I have two  
variables: the dependent variable, Y, and a categorical variable that  
indicates whether the corresponding entry in Y was measured pre- or  
post-intervention. How can I (easily!) convert my data into the y1 x1  
y2 x2 form? (It would be nice if this were to generalise to the case  
where I have measurements on Y at more than two time points.)

2. How do I get "twoway pcspike" to place the correct categorical  
label on the x-axis, rather than the values I used in x1 and x2? I  
can edit the text manually in the graph window, but found that my  
text ran off the edge of the display.

Your help would be very much appreciated.

Chris
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