I am comparing the survival of two unequally sized groups:

Group A, n = 10 000 Group B, n = 50

The analysis is controlled for three variables: p1, p2 and p3. As p3 violates the assumption of proportional hazards, I tried two options to overcome the problem.

1. rcs(p3) - restricted cubic splines did not solve the problem
2. strata(p3_binned) - I binned p3 into four, using quantiles. This solves the problem; however, can I use it when group B's sample size is small and I have 4 predictors in the model?

The model looks as follows:

S ~ group + p1 + p2 + strata(p3_binned)

Edit: p3 has four bins, including number of group B's patients as follows, 6, 9, 10, 16.

I am comparing the survival of two unequally sized groups:

Group A, n = 10 000 Group B, n = 50

The analysis is controlled for three variables: p1, p2 and p3. As p3 violates the assumption of proportional hazards, I tried two options to overcome the problem.

1. rcs(p3) - restricted cubic splines did not solve the problem
2. strata(p3_binned) - I binned p3 into four, using quantiles. This solves the problem; however, can I use it when group B's sample size is small and I have 4 predictors in the model?

The model looks as follows:

S ~ group + p1 + p2 + strata(p3_binned)

Edit 2: p3 has four bins, their sizes and events have given as follows:

• 20 patients, 4 had an event

• 8 patients, 5 had an event

• 13 patients, 8 had an event

• 9 patients, 6 had an event

I am comparing the survival of two unequally sized groups:

Group A, n = 10 000 Group B, n = 50

The analysis is controlled for three variables: p1, p2 and p3. As p3 violates the assumption of proportional hazards, I tried two options to overcome the problem.

1. rcs(p3) - restricted cubic splines did not solve the problem
2. strata(p3_binned) - I binned p3 into four, using quantiles. This solves the problem; however, can I use it when group B's sample size is small and I have 4 predictors in the model?

The model looks as follows:

S ~ group + p1 + p2 + strata(p3_binned)

I am comparing the survival of two unequally sized groups:

Group A, n = 10 000 Group B, n = 50

The analysis is controlled for three variables: p1, p2 and p3. As p3 violates the assumption of proportional hazards, I tried two options to overcome the problem.

1. rcs(p3) - restricted cubic splines did not solve the problem
2. strata(p3_binned) - I binned p3 into four, using quantiles. This solves the problem; however, can I use it when group B's sample size is small and I have 4 predictors in the model?

The model looks as follows:

S ~ group + p1 + p2 + strata(p3_binned)

Edit: p3 has four bins, including number of group B's patients as follows, 6, 9, 10, 16.