1. An apparatus, comprising: a semiconductor substrate having a plurality of die areas and scribe line areas between said die areas; integrated circuit die with active circuit elements for performing a circuit function formed on said die areas; and at least one test module formed in said scribe line areas, said at least one test module including: a reference layout that includes at least one active reference MOS transistor, said active reference MOS transistor having a reference spacing value for each of a plurality of context dependent effect parameters, and a plurality of variant layouts, each of said variant layouts providing at least one active variant MOS transistor that provides a variation with respect to said reference spacing values for at least one of said plurality of context dependent effect parameters.