how to find hazard ratio in spss when do you use cox regression what is the hr in quartile 3 how does the cox regression work in the quartile what is cox regression analysis why does cox regression fail when does cox regression work how do you calculate hazard ratio when calculating hazard ratios spss what to check in a reference group using cox regression can cox regression be used in a study how to calculate cox regression in spss how to find cox regression error in spss what quartile in spss does the reference group have zero events what is cox regression for blood test what is the reference group quartile for cox regression how to do cox regression when does the quartile 1 reference group have zero events? when a quartile does not have any events in the randomized trial, what is the error in spss? which quartile is used for spss