Estimate(s) from the conditional normal distribution based on given parameters
Arguments
rnd
Vector of quantiles
mean
The mean parameter
sd
The sd parameter
lower_bound
The lower bound to be used (current time)
s_obs
is the survival observed up to lower_bound time,
normally defined from time 0 as 1 - pnorm(q = lower_bound, mean, sd) but may be different if parametrization has changed previously