Can anybody help me understand what the negative estimated means in a Poisson regression mean?
I am trying to model the count of damages during transit for 4 different logistics providers. To make it clearer, my dependent variable is the number of times Transit damages have been reported over the past 16 months for different Trucks in service. I have also included an offset variable which is the Logarithm of the number of times the Truck has been in service for the past 16 months(not all trucks have transported goods in all months). My predictor variable is just the category of Trucks, that is to which logistics company the trucks belong. There are 4 companies, which I have coded as 1=AAC,2=DSA,3=OMP and 4=TCI.My reference category is 1=AAC. I am including my detailed SPSS output as follows:
Estimated means are as follows:
Have I done the right thing after all? Also Omnibus and other preliminary tests have been done. Data is a bit under-dispersed with Deviance 0.767 and Pearson Chi Square 0.983.