A method comprising: sampling, by a computing system, a distribution of values describing manufacturing variation for an integrated circuit described by a circuit design; simulating (501; 601), by an analog simulation system of the computing system, the circuit design utilizing the samples of the distribution of the values; determining, by the computing system, when to stop the simulations of the circuit design prior to all of the samples from the distribution having been utilized in the simulations, wherein determining when to stop the simulations of the circuit design further comprises estimating an upper boundary for simulation values for the samples that are remaining to be simulated, and stopping the simulations of the circuit design when the results of the simulations for a current set of the samples exceeds the estimated upper boundary for the simulation values for the samples that are remaining to be simulated; or wherein determining when to stop the simulations of the circuit design comprises identifying , after each simulation of the circuit design, which of the samples have corresponding simulation values falling in a tail of the simulation results, and stopping the simulations after a predetermined number of the simulations having occurred without changing the identification of which of the samples have corresponding simulation values falling in a tail of the simulation results; and utilizing, by the computing system, results of the simulations to characterize operational variation of the circuit design to the manufacturing variation described in the distribution of the values. sampling, by a computing system, a distribution of values describing manufacturing variation for an integrated circuit described by a circuit design; simulating (501; 601), by an analog simulation system of the computing system, the circuit design utilizing the samples of the distribution of the values; determining, by the computing system, when to stop the simulations of the circuit design prior to all of the samples from the distribution having been utilized in the simulations, wherein determining when to stop the simulations of the circuit design further comprises estimating an upper boundary for simulation values for the samples that are remaining to be simulated, and stopping the simulations of the circuit design when the results of the simulations for a current set of the samples exceeds the estimated upper boundary for the simulation values for the samples that are remaining to be simulated; or wherein determining when to stop the simulations of the circuit design comprises identifying , after each simulation of the circuit design, which of the samples have corresponding simulation values falling in a tail of the simulation results, and stopping the simulations after a predetermined number of the simulations having occurred without changing the identification of which of the samples have corresponding simulation values falling in a tail of the simulation results; and utilizing, by the computing system, results of the simulations to characterize operational variation of the circuit design to the manufacturing variation described in the distribution of the values. <EOS>