I need help understanding how to use cox hazzard model to calculate risk of death in data from a cohort study.
I have a set of data on physical activity and I want to do a cox regression on mortality to calculate the risk of death from active time.
I have months from t1 as time, death as status and a selection of numeric data on physical activity.
One set with minutes of low intensity activity
One set with minutes of moderate to high intensity activity
One set with minutes of sedentary time
I also a set of dichotomous data on wether or not the participants fulfilled the recommendations for daily physical.
If I run all of these together as predictor variables, I get different Exp(b) values compared to running only a selection.
Should I run each variable in separate tests and put them together in a table?