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