I am conducting a study on a cohort of people with a follow-up period of 7 years. I wish to use Cox Proportional Hazard model to estimate HR between an exposure and the length of time of an event. One missing information is the date of birth for the all subjects, but month and year are available.This prevents the calculation of exact age at the time of the study.
Any suggestions will be much appreciated? Any sensitivity analysis should be conducted?