I have two groups of patients, let’s say groups A and B, who have the same disease with a well-known genetic cause. My main goal is to see whether there is a difference in survivals by the type of underlying mutation (x and y) in all patients. The sample sizes are ~55:145 for A:B and when I estimate survivals by the group variable, group A has a better survival with log-rank p<0.05. I don’t know what might cause this difference. It may be due to selection bias and possibly some other factors. In this case, would it be appropriate to “pool” these 2 groups with different survivals and compare survivals by gene (x/y) variable in A+B? How would you approach to this question? Thank you!

I have two groups of patients, let’s say groups A and B, who have the same disease with a well-known genetic cause. My main goal is to see whether there is a difference in survivals by the type of underlying mutation (x and y) in all patients. The sample sizes are ~55:145 for A:B and when I estimate survivals by the group variable, group A has a better survival with log-rank p<0.05. I don’t know what might cause this difference. It may be due to selection bias and possibly some other factors. In this case, would it be appropriate to “pool” these 2 groups with different survivals and compare survivals by gene (x/y) variable in A+B? How would you approach this question? Thank you!