Hello Stan community,

I’ve been using the package `brms`

in `R`

to estimate a survival model, I took the following exmaple from another thread:

```
library(simsurv)
library(survival)
set.seed(1234)
# simulated data from the rstanarm::stan_surv example
covs <- data.frame(id = 1:200, trt = stats::rbinom(200, 1L, 0.5))
d1 <- simsurv(lambdas = 0.1,
gammas = 1.5,
betas = c(trt = -0.5),
x = covs,
maxt = 5)
d1 <- merge(d1, covs)
fit_brm <- brm(eventtime | cens(1 - status) ~ 1 + trt,
data = d1, family = brmsfamily("cox"))
```

This example works perfectly, but I want also to estimate the out of sample R^2 with the function `loo_R2`

. The problem is that this function cannot handle the cox family yet. Is there any way to estimate the out of sample R^2 using the Cox family in brms? Any idea or recommendation will be appreciated

Thanks.