I am curious if some one who has played with Zelig for a while knows this. We ran a linear model earlier today that used country fixed effect variables that were collinear. We didn't realize this until running it through stata and seeing that stata's linear regression dropped the 6 relevant independent variables. Further inspection of our zelig output shows that it dropped six of the fixed effect variables created by including as.factor(nation). It then reported the point estimates and other goodies for all specified independent variables and the remaining fixed effect variables. What mechanism does R use to select the best submodel to run once a singularity prevents it from doing its X'X thing. Not a mission-critical question, just curious. thanks, /\llan