intepreting Negative coefficients of Poisson model [duplicate]

i have fitted a Poisson regression to my claim frequency data. my predictor is make of vehicle.

I have obtained the following result:

Coefficients:
Estimate  Std. Error  z value Pr(>|z|)
(Intercept)  -19.99774  1138.82118  -0.018  0.98599
make2         -0.30873    0.20550  -1.502   0.13302
make3         -0.39177    0.21129  -1.854   0.06372
make4         -0.38375    0.13388  -2.866   0.00415 **


How do I interpret the negative coefficients? Thanks

marked as duplicate by COOLSerdash, user88 Feb 23 '14 at 11:30

• You don't mention a link function, which matters for interpretation. From the look of it, I assume it was a log-link. Is that the case? Is make a straight categorical variable - a factor - from which we can take these coefficients to be those going with 0-1 dummies? – Glen_b Feb 23 '14 at 6:09
• On reflection, I am curious to know how you'd interpret positive coefficients in this model, if you had them. I suspect, if negative coefficients are giving you a problem, your notion of the meaning of the positive ones is probably incorrect. – Glen_b Feb 23 '14 at 6:37
• Is this for some subject? – Glen_b Feb 23 '14 at 9:30
• It's kind of amusing that the supposed duplicate was answered by me and I don't think it's a duplicate. Not every question about interpretation has the same answer. I nominated the question for reopening so that perhaps further commentary could be placed on the proper handling of pathological data situations that doe not throw obvious error messages. – DWin Feb 23 '14 at 16:28