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st: Comparing change in rates - frustrating problem, please help


From   Ricardo Ovaldia <[email protected]>
To   [email protected]
Subject   st: Comparing change in rates - frustrating problem, please help
Date   Wed, 28 Jan 2004 13:21:13 -0800 (PST)

Dear Stata users,

This is a basic stat question. In an intervention
trial to increase seat belt use 328 adults were
randomized to either a no intervention group(control)
or an educational intervention. After a few months
they were contacted and asked questions about their
seat belt use. Here is the resulting data:

Pecent seat belt use:
 intervention    before     after
         Yes        29%        58%
          No        40%        52%

The randomization was such that the baseline for the
two groups was NOT the same. How can I correctly test
if the intervention worked given that the baselines
are different and there is a ceiling effect (i.e.
percents can not exceed 100%).

Thank you very much,
Ricardo. 


 


=====
Ricardo Ovaldia, MS
Statistician 
Oklahoma City, OK

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