1. A method of modeling a process, comprising: resolving the process into a plurality of process stages, said plurality of process stages including at least a first process stage and a second process stage; and developing a plurality of models, each corresponding to a respective one of the plurality of process stages, said plurality of models including at least a model of the first process stage and a model of the second process stage; wherein the model corresponding to each process stage is developed using data from one or more runs of that process stage and output quality data relating to the one or more runs of that process stage and wherein the model corresponding to each process stage is adapted to produce an output quality prediction associated with that process stage; and wherein the output quality prediction produced by the model of the first process stage is used to develop the model of the second process stage.