1. A manufacturing process method, comprising the steps of: providing a computer system having a processor and memory and programmed with a simulation model of a manufacturing process, the simulation model when executed by the computer system predicting, in dependence upon a plurality of process input parameters, a value for a performance parameter of a product to be manufactured using the manufacturing process; providing to the computer system an actual value for the product performance parameter of a product actually fabricated during a particular run of the manufacturing process; the computer system estimating, in dependence upon the simulation model and further in dependence upon the actual value for the product performance parameter, values for a calculated subset of the process input parameters that actually existed for the particular run, the estimated values for the calculated subset of the process input parameters being usable for yield management.