Abstract: A computer system (30) and method of operating the same to model worst case performances of an analog circuit is disclosed. The computer system (30) includes disk storage devices for storing a process parameter data base (32), design of the circuit (31), and program instructions for performing the modeling method (33). Under the control of the program instructions, the system computer (22) retrieves the process parameters and desired performances, and performs a designed experiment to determine a Jacobian matrix of the dependence of the performances upon the process parameters. Singular value decomposition of the Jacobian matrix provides a set of singular values and a rotation vector, from which the coefficients of a worst case vector of the process parameters for each of the circuit performances are then derived. The system computer (22) then applies the simulation to the worst case vectors, to evaluate the worst case performances of the designed circuit.