I am currently working on a retrospective analysis where I am looking at patients to see if immune sensitization prior to a procedure has any bearing on outcomes after the procedure. The immune sensitization is a categorical variable (Hi vs Lo).
In regards to outcomes, one of the things I am looking is survival analysis (time to death). I ran a Kaplan-Meier analysis broken down by immune sensitization and there seems to be a statistically significant (p<.05) difference in regards to the time to death.
My questions are these:
- I ran a Cox regression analysis with the sensitization status as the only covariate and noted the p-value to be .35. Why is there such a big difference in the statistical significance and which one should I choose? (if it helps, from a visual inspection, only patients in the Hi category died)
- When analyzing my patient characteristics, I noted that there was a gender difference in the two sensitization categories (p<.05). I ran a Cox Regression model with the sensitization and gender as the covariates and noted that p-value of 0.955 for the sensitization status and 0.5 for the gender. Am I correct in interpreting that neither covariate has any bearing on the time to death?
As requested, here is some of my output
Original Kaplan Meier analysis (PRA_Categ represents the sensitization status):
The Corresponding COX regression with only one covariate (PRA_Categ):
COX regression with two covariates (PRA_Categ and Gender):