1. A method of determining whether or not to perform an action based at least partly on an estimated maximum test range, the method comprising: attaining results generated from a parametric test performed on semiconductor devices included in a control set comprising a subset of a population of semiconductor devices; selecting from among said semiconductor devices at least one extreme subset including at least one of a high-scoring subset including all devices whose results exceed a high cut-off point and a low-scoring subset including all devices whose results fall below a low cut-off point; plotting at least results of said at least one extreme subset as a normal probability plot located between a zero probability axis and a one probability axis; fitting a plurality of curves to a plurality of subsets of said results of said at least one extreme subset respectively; extending each of said plurality of curves to said zero probability axis for said low-scoring subset or to said one probability axis for said high scoring subset thereby to define a corresponding plurality of intersection points along said zero or one probability axis; defining an estimated maximum test range based on at least one of said intersection points; and determining whether or not to perform an action based at least partly on said estimated maximum test range, wherein at least one of said selecting, plotting, fitting, extending, defining or determining is performed by at least one processor.