Hello I am doing a cox regression analysis with ADR as my dependent variable and age, gender, ethnicity, previous hospitalisation, previous falls and expdose1 as my independent variable. Expdose1 is a categorical data with values of 1 to 10. The rest are indicator variables with values of 0 or 1. I am getting an error message coded as r(430) and it also says there is a flat region resulting in a missing likelihood. How do I rectify this?