How to introduce a covariate in a multivariable logistic prediction model when the event of interest always occurs in individuals exposed to this covariate. It is possible to determine the adjusted odds ratio with their 95% confidence interval?
Keeping it simple - If there is no variation in a right-hand-side variable and the dependent variable then your model will fail. A model should seek to explain the variation in Y. If all one of your X's gives you the same Y then there is no variation.