Hi, It is not critical but in case of coxph.null model (~1) extractAIC function generates Warning message: In is.na(fit$coefficients) : is.na() applied to non-(list or vector) of type 'NULL' As I understand it happens because of absent coefficients attribute. Function stats:::extractAIC.coxph Line edf <- sum(!is.na(fit$coefficients)) I think extra null-checking would be useful here. Regards, Andriy ________________________________ Since 1982, Starpoint Solutions has been a trusted source of human capital and solutions. We are committed to our clients, employees, environment, community and social concerns. We foster an inclusive culture based on trust, respect, honesty and solid performance. Learn more about Starpoint and our social responsibility at http://www.starpoint.com/social_responsibility ________________________________ This email message from Starpoint Solutions LLC is for the sole use of the intended recipient(s) and may contain confidential and privileged information. Any unauthorized review, use, disclosure or distribution is prohibited. If you are not the intended recipient, please contact the sender by reply email and destroy all copies of the original message. Opinions, conclusions and other information in this message that do not relate to the official business of Starpoint Solutions shall be understood as neither given nor endorsed by it. [[alternative HTML version deleted]]