Posting on Behalf of Serge Guzy: This is a tip that enables you to simulate uniform random numbers between 0 and 1. This can be useful to simulate events (0 not occurs, 1 occurs) when knowing the probability of occurrence. The algorithm is simple: 1: Simulate a normal random number with mean 0 and standard deviation 1 2: On the resulting output , apply the operator iprobit 3: The result will be a random number uniformly distributed and between 0 and 1 The project is attached and uses the code: test(){ stparm(V = tvV +nV) fixef(tvV = c(, 0, )) ranef(diag(nV) = c(1)) normaltest=V phiinvnormal=iprobit(normaltest) error(CEps = 0.001) observe(CObs =phiinvnormal +0*CEps ) } [file name=sim_0_1_official.phxproj size=802843]Certara | Drug Development Solutions (784 KB)