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From: Vivian Pun on 28 Dec 2009 13:17
Hi,

When I analyze the rate of injury by hospital teaching status. I
calculate the average injury rates by teaching status:
Rate Rate ratio
Teaching 26/1000 FTEs 26/18 = 1.44
Non-teaching 18/1000 FTEs reference

When I fit the data into a Poisson model, an crude univariate
poisson regression model for the association between injury rate and
teaching status shows that the model rate ratio is 1.33. I don't
understand why the crude model rate ratio isn't 1.44 like the observed
rate ratio??? Any thoughts on this? Thank you.

Vivian
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