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In this article the author discusses the challenges regarding the measurement and psychometric assumptions. He discusses professor Stephen Humphry's work regarding the description of an item response theory (IRT) model. He discusses Humphry's measurement assumptions and his views regarding the units underlying the scales and to develop definitions for researchers in the social sciences that mirror definitions used in the physical sciences.

In this article the author discusses professor Stephen Humphry's model of using metrology and physical science analogies to reformulate the relationship between discrimination and the unit. He reports on the metrology program developed by Humphry for humans and social science to follow. He states that Humphry's metrology program require the abandonment of descriptive Rasch models in favor of an explicit causal interpretation of the regression.