Hi,   Thanks for your prompt response.  Yes, I am really concerned about dispersion. However, the only models I know are NB and Poisson.  would you please help me with the SAS code since I couldn't find any source for those models you mentioned. Here is the  SAS code.   proc genmod data=odot.crossover; model C_F_P = lnaadt Installation_length__miles_ Number_of_Lanes / dist=poisson link=log; run;   ... View more