NLME runs provide you several outputs. One of the text output is the core status that summarizes the model settings and the results. At the top of the core status file for QRPEM engine runs there is a listing such as # Population: IMPEM engine log file MAX ITERS = 1000 Importance sample size = 300 SIR sample size = 10 impsampdof= 0 QRPEM quasirandom sampling used Owen scrambling used (option 1) expfac_envelope= 1.35720881 MAP assistance off The exp_fac envelope number is the expansion factor by which the cholesky factor of the covariance matrix of the Posterior is expanded to get the cholesky factor of the importance samping distribution (so cov(importance dist) = exp_fac*2 cov(posterior) (exp_fac is short for expansion factor) This is determined by the acceptance ratio and the number of random effects leneta by the formula Exp_fac = accratio(-1.d0/dfloat(leneta)) This is the same formula used by NONMEM,