A simulated data set under left truncation but no right censoring.
The left truncation time and the event time are dependent via the two covariates `Z1' and `Z2'.
Under the data generating mechanism,
the conditional distribution of the event time given covariates follows a Cox proportional hazards model in the full data, and
the conditional distribution of the left truncation time given covariates follows a Cox proportional hazards model on the reversed time scale in the full data.
The truncation rate is 29.5%;
and the truth \(P^*(T>3) = 0.5755753\).