Dear  R  helpers,
running the following code of a glm model of the family poisson, gives
predicted values < 0. Why?

library(MASS)
library(stats)
library(mvtnorm)
library(pscl)
data(bioChemists)
poisson_glm <-  glm(art ~ fem + mar + kid5 + phd + ment, data = bioChemists,
family = poisson)
predicted.values = predict(poisson_glm)
range(predicted.values)


Thank you in advance for any hints.
Best regards,
P. Olsson

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