Re: stats help: comparing two proportions
- From: Ryan <Ryan.Andrew.Black@xxxxxxxxx>
- Date: Tue, 22 Jul 2008 06:23:02 -0700 (PDT)
On Jul 21, 10:57 am, hvanderkloos...@xxxxxxxxx wrote:
Hello,
I am trying to compare two proportions and I am wondering what
statistical test is best? Here is an overview of my data:
I have:
the number of events pre-intervention
the number of events post-intervention
**the subjects in the pre and post intervention groups are NOT the
same people... the intervention was community-based and we measured
the number of times "x" occurred in the pre intervention time period
and the number of times "x" occurred in the post intervention time
period.
We want to compare the number of events pre intervention to the number
that occurred post intervention such that we can say the intervention
worked. Is comparing the two proportions the best way to do this? Is
there a better way? Also, what SAS procedure would I use?
Thanks all.
H. van der Klooster
I was certain I responded to this post yesterday. I guess it didn't go
through. Anyway, I could certainly be wrong, but I think you want to
run a test of *independent* proportions (either chi-square or z).
Visually, I think this is what you're saying....
Time
-------------
Pre Post
-------------
Yes A B
Event -------------
No C D
Here's a link to an online calculator for the z-test:
http://www.dimensionresearch.com/resources/calculators/ztest.html
Ryan
.
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