1. A method of simulating the degradation of a circuit, comprising: providing a netlist specifying the components of the circuit; supplying a plurality of circuit stress time values; supplying aging model information on selected ones of the components; simulating the behavior of the fresh circuit to determine for each of the selected components a component degradation parameter relative to circuit stress time; and determining the degraded operation of the circuit by simulating the operation of the circuit with the specified components using their respective aging model information and respective relative component degradation parameter at the supplied circuit stress time values.